Remove ofy scaffolding from DomainContent and core classes (#1660)

This removes the code that converts between ofy fields and SQL fields in DomainContent and a number of related core classes (basically anything that also needed modification to support the removal from DomainContent).

core/src/main/java/google/registry/flows/contact/ContactFlowUtils.java

@@ -26,6 +26,7 @@ import google.registry.flows.EppException.ParameterValuePolicyErrorException;
 import google.registry.flows.EppException.ParameterValueSyntaxErrorException;
 import google.registry.model.contact.ContactAddress;
 import google.registry.model.contact.ContactHistory;
+import google.registry.model.contact.ContactHistory.ContactHistoryId;
 import google.registry.model.contact.ContactResource;
 import google.registry.model.contact.PostalInfo;
 import google.registry.model.poll.PendingActionNotificationResponse.ContactPendingActionNotificationResponse;
@@ -84,7 +85,9 @@ public class ContactFlowUtils {
                     transferData.getTransferStatus().isApproved(),
                     transferData.getTransferRequestTrid(),
                     now)))
-        .setParentKey(contactHistoryKey)
+        .setContactHistoryId(
+            new ContactHistoryId(
+                contactHistoryKey.getParent().getName(), contactHistoryKey.getId()))
         .build();
   }
 
@@ -96,7 +99,9 @@ public class ContactFlowUtils {
         .setEventTime(transferData.getPendingTransferExpirationTime())
         .setMsg(transferData.getTransferStatus().getMessage())
         .setResponseData(ImmutableList.of(createTransferResponse(targetId, transferData)))
-        .setParentKey(contactHistoryKey)
+        .setContactHistoryId(
+            new ContactHistoryId(
+                contactHistoryKey.getParent().getName(), contactHistoryKey.getId()))
         .build();
   }
 

core/src/main/java/google/registry/flows/contact/ContactTransferRequestFlow.java

@@ -134,6 +134,8 @@ public final class ContactTransferRequestFlow implements TransactionalFlow {
             .asBuilder()
             .setTransferStatus(TransferStatus.PENDING)
             .setServerApproveEntities(
+                serverApproveGainingPollMessage.getContactRepoId(),
+                contactHistoryKey.getId(),
                 ImmutableSet.of(
                     serverApproveGainingPollMessage.createVKey(),
                     serverApproveLosingPollMessage.createVKey()))

core/src/main/java/google/registry/flows/domain/DomainCreateFlow.java

@@ -87,6 +87,7 @@ import google.registry.model.domain.DomainBase;
 import google.registry.model.domain.DomainCommand;
 import google.registry.model.domain.DomainCommand.Create;
 import google.registry.model.domain.DomainHistory;
+import google.registry.model.domain.DomainHistory.DomainHistoryId;
 import google.registry.model.domain.GracePeriod;
 import google.registry.model.domain.Period;
 import google.registry.model.domain.fee.FeeCreateCommandExtension;
@@ -357,7 +358,8 @@ public final class DomainCreateFlow implements TransactionalFlow {
             .setIdnTableName(validateDomainNameWithIdnTables(domainName))
             .setRegistrationExpirationTime(registrationExpirationTime)
             .setAutorenewBillingEvent(autorenewBillingEvent.createVKey())
-            .setAutorenewPollMessage(autorenewPollMessage.createVKey())
+            .setAutorenewPollMessage(
+                autorenewPollMessage.createVKey(), autorenewPollMessage.getHistoryRevisionId())
             .setLaunchNotice(hasClaimsNotice ? launchCreate.get().getNotice() : null)
             .setSmdId(signedMarkId)
             .setDsData(secDnsCreate.map(SecDnsCreateExtension::getDsData).orElse(null))
@@ -576,7 +578,8 @@ public final class DomainCreateFlow implements TransactionalFlow {
         .setRegistrarId(registrarId)
         .setEventTime(registrationExpirationTime)
         .setMsg("Domain was auto-renewed.")
-        .setParentKey(domainHistoryKey)
+        .setDomainHistoryId(
+            new DomainHistoryId(domainHistoryKey.getParent().getName(), domainHistoryKey.getId()))
         .build();
   }
 
@@ -608,7 +611,7 @@ public final class DomainCreateFlow implements TransactionalFlow {
             ImmutableList.of(
                 DomainPendingActionNotificationResponse.create(
                     fullyQualifiedDomainName, true, historyEntry.getTrid(), now)))
-        .setParent(historyEntry)
+        .setHistoryEntry(historyEntry)
         .build();
   }
 

core/src/main/java/google/registry/flows/domain/DomainDeleteFlow.java

@@ -66,6 +66,7 @@ import google.registry.model.ImmutableObject;
 import google.registry.model.billing.BillingEvent;
 import google.registry.model.domain.DomainBase;
 import google.registry.model.domain.DomainHistory;
+import google.registry.model.domain.DomainHistory.DomainHistoryId;
 import google.registry.model.domain.GracePeriod;
 import google.registry.model.domain.fee.BaseFee.FeeType;
 import google.registry.model.domain.fee.Credit;
@@ -355,7 +356,8 @@ public final class DomainDeleteFlow implements TransactionalFlow {
             ImmutableList.of(
                 DomainPendingActionNotificationResponse.create(
                     existingDomain.getDomainName(), true, trid, deletionTime)))
-        .setParentKey(domainHistoryKey)
+        .setDomainHistoryId(
+            new DomainHistoryId(domainHistoryKey.getParent().getName(), domainHistoryKey.getId()))
         .build();
   }
 
@@ -367,7 +369,8 @@ public final class DomainDeleteFlow implements TransactionalFlow {
     return new PollMessage.OneTime.Builder()
         .setRegistrarId(existingDomain.getPersistedCurrentSponsorRegistrarId())
         .setEventTime(now)
-        .setParentKey(domainHistoryKey)
+        .setDomainHistoryId(
+            new DomainHistoryId(domainHistoryKey.getParent().getName(), domainHistoryKey.getId()))
         .setMsg(
             String.format(
                 "Domain %s was deleted by registry administrator with final deletion effective: %s",

core/src/main/java/google/registry/flows/domain/DomainFlowUtils.java

@@ -63,7 +63,6 @@ import com.google.common.collect.Multimaps;
 import com.google.common.collect.Sets;
 import com.google.common.collect.Streams;
 import com.google.common.net.InternetDomainName;
-import com.googlecode.objectify.Key;
 import google.registry.flows.EppException;
 import google.registry.flows.EppException.AuthorizationErrorException;
 import google.registry.flows.EppException.CommandUseErrorException;
@@ -89,6 +88,7 @@ import google.registry.model.domain.DomainCommand.CreateOrUpdate;
 import google.registry.model.domain.DomainCommand.InvalidReferencesException;
 import google.registry.model.domain.DomainCommand.Update;
 import google.registry.model.domain.DomainHistory;
+import google.registry.model.domain.DomainHistory.DomainHistoryId;
 import google.registry.model.domain.ForeignKeyedDesignatedContact;
 import google.registry.model.domain.Period;
 import google.registry.model.domain.fee.BaseFee;
@@ -592,14 +592,15 @@ public class DomainFlowUtils {
     // where all autorenew poll messages had already been delivered (this would cause the poll
     // message to be deleted), and then subsequently the transfer was canceled, rejected, or deleted
     // (which would cause the poll message to be recreated here).
-    Key<PollMessage.Autorenew> existingAutorenewKey = domain.getAutorenewPollMessage().getOfyKey();
     PollMessage.Autorenew updatedAutorenewPollMessage =
         autorenewPollMessage.isPresent()
             ? autorenewPollMessage.get().asBuilder().setAutorenewEndTime(newEndTime).build()
             : newAutorenewPollMessage(domain)
-                .setId(existingAutorenewKey.getId())
+                .setId((Long) domain.getAutorenewPollMessage().getSqlKey())
                 .setAutorenewEndTime(newEndTime)
-                .setParentKey(existingAutorenewKey.getParent())
+                .setDomainHistoryId(
+                    new DomainHistoryId(
+                        domain.getRepoId(), domain.getAutorenewPollMessageHistoryId()))
                 .build();
 
     // If the resultant autorenew poll message would have no poll messages to deliver, then just

core/src/main/java/google/registry/flows/domain/DomainRenewFlow.java

@@ -58,6 +58,7 @@ import google.registry.model.billing.BillingEvent.Recurring;
 import google.registry.model.domain.DomainBase;
 import google.registry.model.domain.DomainCommand.Renew;
 import google.registry.model.domain.DomainHistory;
+import google.registry.model.domain.DomainHistory.DomainHistoryId;
 import google.registry.model.domain.DomainRenewData;
 import google.registry.model.domain.GracePeriod;
 import google.registry.model.domain.Period;
@@ -187,7 +188,9 @@ public final class DomainRenewFlow implements TransactionalFlow {
     PollMessage.Autorenew newAutorenewPollMessage =
         newAutorenewPollMessage(existingDomain)
             .setEventTime(newExpirationTime)
-            .setParentKey(domainHistoryKey)
+            .setDomainHistoryId(
+                new DomainHistoryId(
+                    domainHistoryKey.getParent().getName(), domainHistoryKey.getId()))
             .build();
     // End the old autorenew billing event and poll message now. This may delete the poll message.
     updateAutorenewRecurrenceEndTime(existingDomain, now);
@@ -198,7 +201,9 @@ public final class DomainRenewFlow implements TransactionalFlow {
             .setLastEppUpdateRegistrarId(registrarId)
             .setRegistrationExpirationTime(newExpirationTime)
             .setAutorenewBillingEvent(newAutorenewEvent.createVKey())
-            .setAutorenewPollMessage(newAutorenewPollMessage.createVKey())
+            .setAutorenewPollMessage(
+                newAutorenewPollMessage.createVKey(),
+                newAutorenewPollMessage.getHistoryRevisionId())
             .addGracePeriod(
                 GracePeriod.forBillingEvent(
                     GracePeriodStatus.RENEW, existingDomain.getRepoId(), explicitRenewEvent))

core/src/main/java/google/registry/flows/domain/DomainRestoreRequestFlow.java

@@ -53,6 +53,7 @@ import google.registry.model.billing.BillingEvent.Reason;
 import google.registry.model.domain.DomainBase;
 import google.registry.model.domain.DomainCommand.Update;
 import google.registry.model.domain.DomainHistory;
+import google.registry.model.domain.DomainHistory.DomainHistoryId;
 import google.registry.model.domain.fee.BaseFee.FeeType;
 import google.registry.model.domain.fee.Fee;
 import google.registry.model.domain.fee.FeeTransformResponseExtension;
@@ -173,7 +174,9 @@ public final class DomainRestoreRequestFlow implements TransactionalFlow {
         newAutorenewPollMessage(existingDomain)
             .setEventTime(newExpirationTime)
             .setAutorenewEndTime(END_OF_TIME)
-            .setParentKey(domainHistoryKey)
+            .setDomainHistoryId(
+                new DomainHistoryId(
+                    domainHistoryKey.getParent().getName(), domainHistoryKey.getId()))
             .build();
     DomainBase newDomain =
         performRestore(
@@ -245,7 +248,8 @@ public final class DomainRestoreRequestFlow implements TransactionalFlow {
         .setGracePeriods(null)
         .setDeletePollMessage(null)
         .setAutorenewBillingEvent(autorenewEvent.createVKey())
-        .setAutorenewPollMessage(autorenewPollMessage.createVKey())
+        .setAutorenewPollMessage(
+            autorenewPollMessage.createVKey(), autorenewPollMessage.getHistoryRevisionId())
         // Clear the autorenew end time so if it had expired but is now explicitly being restored,
         // it won't immediately be deleted again.
         .setAutorenewEndTime(Optional.empty())

core/src/main/java/google/registry/flows/domain/DomainTransferApproveFlow.java

@@ -51,6 +51,7 @@ import google.registry.model.billing.BillingEvent.Flag;
 import google.registry.model.billing.BillingEvent.Reason;
 import google.registry.model.domain.DomainBase;
 import google.registry.model.domain.DomainHistory;
+import google.registry.model.domain.DomainHistory.DomainHistoryId;
 import google.registry.model.domain.GracePeriod;
 import google.registry.model.domain.metadata.MetadataExtension;
 import google.registry.model.domain.rgp.GracePeriodStatus;
@@ -176,7 +177,9 @@ public final class DomainTransferApproveFlow implements TransactionalFlow {
             .setEventTime(newExpirationTime)
             .setAutorenewEndTime(END_OF_TIME)
             .setMsg("Domain was auto-renewed.")
-            .setParentKey(domainHistoryKey)
+            .setDomainHistoryId(
+                new DomainHistoryId(
+                    domainHistoryKey.getParent().getName(), domainHistoryKey.getId()))
             .build();
     // Construct the post-transfer domain.
     DomainBase partiallyApprovedDomain =
@@ -194,7 +197,9 @@ public final class DomainTransferApproveFlow implements TransactionalFlow {
                     .build())
             .setRegistrationExpirationTime(newExpirationTime)
             .setAutorenewBillingEvent(autorenewEvent.createVKey())
-            .setAutorenewPollMessage(gainingClientAutorenewPollMessage.createVKey())
+            .setAutorenewPollMessage(
+                gainingClientAutorenewPollMessage.createVKey(),
+                gainingClientAutorenewPollMessage.getHistoryRevisionId())
             // Remove all the old grace periods and add a new one for the transfer.
             .setGracePeriods(
                 billingEvent

core/src/main/java/google/registry/flows/domain/DomainTransferRequestFlow.java

@@ -208,6 +208,8 @@ public final class DomainTransferRequestFlow implements TransactionalFlow {
     // Create the transfer data that represents the pending transfer.
     DomainTransferData pendingTransferData =
         createPendingTransferData(
+            domainAtTransferTime.getRepoId(),
+            domainHistoryKey.getId(),
             new DomainTransferData.Builder()
                 .setTransferRequestTrid(trid)
                 .setTransferRequestTime(now)

core/src/main/java/google/registry/flows/domain/DomainTransferUtils.java

@@ -26,6 +26,7 @@ import google.registry.model.billing.BillingEvent.Flag;
 import google.registry.model.billing.BillingEvent.Reason;
 import google.registry.model.domain.DomainBase;
 import google.registry.model.domain.DomainHistory;
+import google.registry.model.domain.DomainHistory.DomainHistoryId;
 import google.registry.model.domain.GracePeriod;
 import google.registry.model.domain.Period;
 import google.registry.model.domain.rgp.GracePeriodStatus;
@@ -51,6 +52,8 @@ public final class DomainTransferUtils {
 
   /** Sets up {@link TransferData} for a domain with links to entities for server approval. */
   public static DomainTransferData createPendingTransferData(
+      String domainRepoId,
+      Long historyId,
       DomainTransferData.Builder transferDataBuilder,
       ImmutableSet<TransferServerApproveEntity> serverApproveEntities,
       Period transferPeriod) {
@@ -82,7 +85,7 @@ public final class DomainTransferUtils {
                 .map(PollMessage.Autorenew.class::cast)
                 .collect(onlyElement())
                 .createVKey())
-        .setServerApproveEntities(serverApproveEntityKeys.build())
+        .setServerApproveEntities(domainRepoId, historyId, serverApproveEntityKeys.build())
         .setTransferPeriod(transferPeriod)
         .build();
   }
@@ -180,7 +183,8 @@ public final class DomainTransferUtils {
                     transferData.getTransferStatus().isApproved(),
                     transferData.getTransferRequestTrid(),
                     now)))
-        .setParentKey(domainHistoryKey)
+        .setDomainHistoryId(
+            new DomainHistoryId(domainHistoryKey.getParent().getName(), domainHistoryKey.getId()))
         .build();
   }
 
@@ -197,7 +201,8 @@ public final class DomainTransferUtils {
         .setResponseData(
             ImmutableList.of(
                 createTransferResponse(targetId, transferData, extendedRegistrationExpirationTime)))
-        .setParentKey(domainHistoryKey)
+        .setDomainHistoryId(
+            new DomainHistoryId(domainHistoryKey.getParent().getName(), domainHistoryKey.getId()))
         .build();
   }
 
@@ -228,7 +233,8 @@ public final class DomainTransferUtils {
         .setEventTime(serverApproveNewExpirationTime)
         .setAutorenewEndTime(END_OF_TIME)
         .setMsg("Domain was auto-renewed.")
-        .setParentKey(domainHistoryKey)
+        .setDomainHistoryId(
+            new DomainHistoryId(domainHistoryKey.getParent().getName(), domainHistoryKey.getId()))
         .build();
   }
 

core/src/main/java/google/registry/flows/domain/DomainUpdateFlow.java

@@ -66,6 +66,7 @@ import google.registry.flows.domain.DomainFlowUtils.NameserversNotSpecifiedForTl
 import google.registry.model.ImmutableObject;
 import google.registry.model.billing.BillingEvent;
 import google.registry.model.billing.BillingEvent.Reason;
+import google.registry.model.domain.DesignatedContact;
 import google.registry.model.domain.DomainBase;
 import google.registry.model.domain.DomainCommand.Update;
 import google.registry.model.domain.DomainCommand.Update.AddRemove;
@@ -243,6 +244,13 @@ public final class DomainUpdateFlow implements TransactionalFlow {
     validateRegistrantIsntBeingRemoved(change);
     Optional<SecDnsUpdateExtension> secDnsUpdate =
         eppInput.getSingleExtension(SecDnsUpdateExtension.class);
+
+    // We have to verify no duplicate contacts _before_ constructing the domain because it is
+    // illegal to construct a domain with duplicate contacts.
+    Sets.SetView<DesignatedContact> newContacts =
+        Sets.union(Sets.difference(domain.getContacts(), remove.getContacts()), add.getContacts());
+    validateNoDuplicateContacts(newContacts);
+
     DomainBase.Builder domainBuilder =
         domain
             .asBuilder()
@@ -263,8 +271,8 @@ public final class DomainUpdateFlow implements TransactionalFlow {
             .removeStatusValues(remove.getStatusValues())
             .addNameservers(add.getNameservers().stream().collect(toImmutableSet()))
             .removeNameservers(remove.getNameservers().stream().collect(toImmutableSet()))
-            .addContacts(add.getContacts())
             .removeContacts(remove.getContacts())
+            .addContacts(add.getContacts())
             .setRegistrant(firstNonNull(change.getRegistrant(), domain.getRegistrant()))
             .setAuthInfo(firstNonNull(change.getAuthInfo(), domain.getAuthInfo()));
     Optional<DomainUpdateSuperuserExtension> superuserExt =
@@ -286,7 +294,6 @@ public final class DomainUpdateFlow implements TransactionalFlow {
   }
 
   private void validateNewState(DomainBase newDomain) throws EppException {
-    validateNoDuplicateContacts(newDomain.getContacts());
     validateRequiredContactsPresent(newDomain.getRegistrant(), newDomain.getContacts());
     validateDsData(newDomain.getDsData());
     validateNameserversCountForTld(
@@ -360,7 +367,7 @@ public final class DomainUpdateFlow implements TransactionalFlow {
 
     return Optional.ofNullable(
         new PollMessage.OneTime.Builder()
-            .setParent(historyEntry)
+            .setHistoryEntry(historyEntry)
             .setEventTime(now)
             .setRegistrarId(existingDomain.getCurrentSponsorRegistrarId())
             .setMsg(msg)

core/src/main/java/google/registry/model/EppResourceUtils.java

@@ -226,7 +226,7 @@ public final class EppResourceUtils {
     checkArgument(TransferStatus.PENDING.equals(transferData.getTransferStatus()));
     TransferData.Builder transferDataBuilder = transferData.asBuilder();
     transferDataBuilder.setTransferStatus(TransferStatus.SERVER_APPROVED);
-    transferDataBuilder.setServerApproveEntities(null);
+    transferDataBuilder.setServerApproveEntities(null, null, null);
     if (transferData instanceof DomainTransferData) {
       ((DomainTransferData.Builder) transferDataBuilder)
           .setServerApproveBillingEvent(null)

core/src/main/java/google/registry/model/ResourceTransferUtils.java

@@ -128,7 +128,7 @@ public final class ResourceTransferUtils {
                           createTransferResponse(newResource, newResource.getTransferData()),
                           createPendingTransferNotificationResponse(
                               resource, oldTransferData.getTransferRequestTrid(), false, now)))
-                  .setParent(historyEntry)
+                  .setHistoryEntry(historyEntry)
                   .build());
     }
   }

core/src/main/java/google/registry/model/contact/ContactHistory.java

@@ -84,6 +84,10 @@ public class ContactHistory extends HistoryEntry implements UnsafeSerializable {
     return super.getId();
   }
 
+  public ContactHistoryId getContactHistoryId() {
+    return new ContactHistoryId(getContactRepoId(), getId());
+  }
+
   /**
    * The values of all the fields on the {@link ContactBase} object after the action represented by
    * this history object was executed.
@@ -147,8 +151,7 @@ public class ContactHistory extends HistoryEntry implements UnsafeSerializable {
      *
      * <p>This method is private because it is only used by Hibernate.
      */
-    @SuppressWarnings("unused")
+    public String getContactRepoId() {
-    private String getContactRepoId() {
       return contactRepoId;
     }
 
@@ -157,8 +160,7 @@ public class ContactHistory extends HistoryEntry implements UnsafeSerializable {
      *
      * <p>This method is private because it is only used by Hibernate.
      */
-    @SuppressWarnings("unused")
+    public long getId() {
-    private long getId() {
       return id;
     }
 

core/src/main/java/google/registry/model/domain/DomainBase.java

@@ -150,9 +150,7 @@ public class DomainBase extends DomainContent implements ForeignKeyedEppResource
 
   /** Post-load method to eager load the collections. */
   @PostLoad
-  @Override
   protected void postLoad() {
-    super.postLoad();
     // TODO(b/188044616): Determine why Eager loading doesn't work here.
     Hibernate.initialize(dsData);
     Hibernate.initialize(gracePeriods);
@@ -190,7 +188,9 @@ public class DomainBase extends DomainContent implements ForeignKeyedEppResource
     public Builder copyFrom(DomainContent domainContent) {
       this.getInstance().copyUpdateTimestamp(domainContent);
       return this.setAuthInfo(domainContent.getAuthInfo())
-          .setAutorenewPollMessage(domainContent.getAutorenewPollMessage())
+          .setAutorenewPollMessage(
+              domainContent.getAutorenewPollMessage(),
+              domainContent.getAutorenewPollMessageHistoryId())
           .setAutorenewBillingEvent(domainContent.getAutorenewBillingEvent())
           .setAutorenewEndTime(domainContent.getAutorenewEndTime())
           .setContacts(domainContent.getContacts())

core/src/main/java/google/registry/model/domain/DomainContent.java

@@ -42,12 +42,10 @@ import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.ImmutableSortedSet;
 import com.google.common.collect.Ordering;
 import com.google.common.collect.Sets;
-import com.google.common.collect.Streams;
 import com.googlecode.objectify.Key;
 import com.googlecode.objectify.annotation.Ignore;
 import com.googlecode.objectify.annotation.IgnoreSave;
 import com.googlecode.objectify.annotation.Index;
-import com.googlecode.objectify.annotation.OnLoad;
 import com.googlecode.objectify.condition.IfNull;
 import google.registry.dns.RefreshDnsAction;
 import google.registry.flows.ResourceFlowUtils;
@@ -82,7 +80,6 @@ import javax.persistence.Column;
 import javax.persistence.Embeddable;
 import javax.persistence.Embedded;
 import javax.persistence.MappedSuperclass;
-import javax.persistence.PostLoad;
 import javax.persistence.Transient;
 import org.hibernate.collection.internal.PersistentSet;
 import org.joda.time.DateTime;
@@ -139,23 +136,12 @@ public class DomainContent extends EppResource
   /** References to hosts that are the nameservers for the domain. */
   @EmptySetToNull @Index @Transient Set<VKey<HostResource>> nsHosts;
 
-  /**
+  /** Contacts. */
-   * The union of the contacts visible via {@link #getContacts} and {@link #getRegistrant}.
+  VKey<ContactResource> adminContact;
-   *
-   * <p>These are stored in one field so that we can query across all contacts at once.
-   */
-  @Transient Set<DesignatedContact> allContacts;
 
-  /**
+  VKey<ContactResource> billingContact;
-   * Contacts as they are stored in cloud SQL.
+  VKey<ContactResource> techContact;
-   *
+  VKey<ContactResource> registrantContact;
-   * <p>This information is duplicated in allContacts, and must be kept in sync with it.
-   */
-  @Ignore VKey<ContactResource> adminContact;
-
-  @Ignore VKey<ContactResource> billingContact;
-  @Ignore VKey<ContactResource> techContact;
-  @Ignore VKey<ContactResource> registrantContact;
 
   /** Authorization info (aka transfer secret) of the domain. */
   @Embedded
@@ -165,12 +151,7 @@ public class DomainContent extends EppResource
   })
   DomainAuthInfo authInfo;
 
-  /**
+  /** Data used to construct DS records for this domain. */
-   * Data used to construct DS records for this domain.
-   *
-   * <p>This is {@literal @}XmlTransient because it needs to be returned under the "extension" tag
-   * of an info response rather than inside the "infData" tag.
-   */
   @Transient Set<DelegationSignerData> dsData;
 
   /**
@@ -178,7 +159,6 @@ public class DomainContent extends EppResource
    *
    * <p>It's {@literal @}XmlTransient because it's not returned in an info response.
    */
-  @IgnoreSave(IfNull.class)
   @Embedded
   @AttributeOverrides({
     @AttributeOverride(name = "noticeId.tcnId", column = @Column(name = "launch_notice_tcn_id")),
@@ -218,15 +198,6 @@ public class DomainContent extends EppResource
   @Column(name = "deletion_poll_message_id")
   VKey<PollMessage.OneTime> deletePollMessage;
 
-  /**
-   * History record for the delete poll message.
-   *
-   * <p>Here so we can restore the original ofy key from sql.
-   */
-  @Column(name = "deletion_poll_message_history_id")
-  @Ignore
-  Long deletePollMessageHistoryId;
-
   /**
    * The recurring billing event associated with this domain's autorenewals.
    *
@@ -238,15 +209,6 @@ public class DomainContent extends EppResource
   @Column(name = "billing_recurrence_id")
   VKey<BillingEvent.Recurring> autorenewBillingEvent;
 
-  /**
-   * History record for the autorenew billing event.
-   *
-   * <p>Here so we can restore the original ofy key from sql.
-   */
-  @Column(name = "billing_recurrence_history_id")
-  @Ignore
-  Long autorenewBillingEventHistoryId;
-
   /**
    * The recurring poll message associated with this domain's autorenewals.
    *
@@ -332,75 +294,6 @@ public class DomainContent extends EppResource
     return Optional.ofNullable(dnsRefreshRequestTime);
   }
 
-  @OnLoad
-  void load() {
-    // Reconstitute all of the contacts so that they have VKeys.
-    allContacts =
-        allContacts.stream().map(DesignatedContact::reconstitute).collect(toImmutableSet());
-    setContactFields(allContacts, true);
-
-    // We have to return the cloned object here because the original object's hashcode is not
-    // correct due to the change to its domainRepoId and history ids. The cloned object will have a
-    // null hashcode so that it can get a recalculated hashcode when its hashCode() is invoked.
-    // TODO(b/162739503): Remove this after fully migrating to Cloud SQL.
-    gracePeriods =
-        nullToEmptyImmutableCopy(gracePeriods).stream()
-            .map(gracePeriod -> gracePeriod.cloneAfterOfyLoad(getRepoId()))
-            .collect(toImmutableSet());
-
-    // Restore history record ids.
-    autorenewPollMessageHistoryId = getHistoryId(autorenewPollMessage);
-    autorenewBillingEventHistoryId = getHistoryId(autorenewBillingEvent);
-    deletePollMessageHistoryId = getHistoryId(deletePollMessage);
-
-    // Fix PollMessage VKeys.
-    autorenewPollMessage = PollMessage.Autorenew.convertVKey(autorenewPollMessage);
-    deletePollMessage = PollMessage.OneTime.convertVKey(deletePollMessage);
-
-    dsData =
-        nullToEmptyImmutableCopy(dsData).stream()
-            .map(dsData -> dsData.cloneWithDomainRepoId(getRepoId()))
-            .collect(toImmutableSet());
-
-    if (transferData != null) {
-      transferData.convertVKeys();
-    }
-  }
-
-  @PostLoad
-  protected void postLoad() {
-    // Reconstitute the contact list.
-    ImmutableSet.Builder<DesignatedContact> contactsBuilder = new ImmutableSet.Builder<>();
-
-    if (registrantContact != null) {
-      contactsBuilder.add(
-          DesignatedContact.create(DesignatedContact.Type.REGISTRANT, registrantContact));
-    }
-    if (billingContact != null) {
-      contactsBuilder.add(DesignatedContact.create(DesignatedContact.Type.BILLING, billingContact));
-    }
-    if (techContact != null) {
-      contactsBuilder.add(DesignatedContact.create(DesignatedContact.Type.TECH, techContact));
-    }
-    if (adminContact != null) {
-      contactsBuilder.add(DesignatedContact.create(DesignatedContact.Type.ADMIN, adminContact));
-    }
-
-    allContacts = contactsBuilder.build();
-
-    // Reconstitute the composite ofy keys from the SQL data.
-    Key<DomainBase> myKey = Key.create(DomainBase.class, getRepoId());
-    deletePollMessage = restoreOfyFrom(myKey, deletePollMessage, deletePollMessageHistoryId);
-    autorenewBillingEvent =
-        restoreOfyFrom(myKey, autorenewBillingEvent, autorenewBillingEventHistoryId);
-    autorenewPollMessage =
-        restoreOfyFrom(myKey, autorenewPollMessage, autorenewPollMessageHistoryId);
-
-    if (transferData != null) {
-      transferData.restoreOfyKeys(myKey);
-    }
-  }
-
   public static <T> VKey<T> restoreOfyFrom(Key<DomainBase> domainKey, VKey<T> key, Long historyId) {
     if (historyId == null) {
       // This is a legacy key (or a null key, in which case this works too)
@@ -430,6 +323,10 @@ public class DomainContent extends EppResource
     return autorenewPollMessage;
   }
 
+  public Long getAutorenewPollMessageHistoryId() {
+    return autorenewPollMessageHistoryId;
+  }
+
   public ImmutableSet<GracePeriod> getGracePeriods() {
     return nullToEmptyImmutableCopy(gracePeriods);
   }
@@ -609,7 +506,9 @@ public class DomainContent extends EppResource
               // Set the speculatively-written new autorenew events as the domain's autorenew
               // events.
               .setAutorenewBillingEvent(transferData.getServerApproveAutorenewEvent())
-              .setAutorenewPollMessage(transferData.getServerApproveAutorenewPollMessage());
+              .setAutorenewPollMessage(
+                  transferData.getServerApproveAutorenewPollMessage(),
+                  transferData.getServerApproveAutorenewPollMessageHistoryId());
       if (transferData.getTransferPeriod().getValue() == 1) {
         // Set the grace period using a key to the prescheduled transfer billing event.  Not using
         // GracePeriod.forBillingEvent() here in order to avoid the actual Datastore fetch.
@@ -731,9 +630,7 @@ public class DomainContent extends EppResource
 
   /** Associated contacts for the domain (other than registrant). */
   public ImmutableSet<DesignatedContact> getContacts() {
-    return nullToEmpty(allContacts).stream()
+    return getAllContacts(false);
-        .filter(IS_REGISTRANT.negate())
-        .collect(toImmutableSet());
   }
 
   public DomainAuthInfo getAuthInfo() {
@@ -742,12 +639,29 @@ public class DomainContent extends EppResource
 
   /** Returns all referenced contacts from this domain. */
   public ImmutableSet<VKey<ContactResource>> getReferencedContacts() {
-    return nullToEmptyImmutableCopy(allContacts).stream()
+    return nullToEmptyImmutableCopy(getAllContacts(true)).stream()
         .map(DesignatedContact::getContactKey)
         .filter(Objects::nonNull)
         .collect(toImmutableSet());
   }
 
+  private ImmutableSet<DesignatedContact> getAllContacts(boolean includeRegistrant) {
+    ImmutableSet.Builder<DesignatedContact> builder = new ImmutableSet.Builder<>();
+    if (includeRegistrant && registrantContact != null) {
+      builder.add(DesignatedContact.create(DesignatedContact.Type.REGISTRANT, registrantContact));
+    }
+    if (adminContact != null) {
+      builder.add(DesignatedContact.create(DesignatedContact.Type.ADMIN, adminContact));
+    }
+    if (billingContact != null) {
+      builder.add(DesignatedContact.create(DesignatedContact.Type.BILLING, billingContact));
+    }
+    if (techContact != null) {
+      builder.add(DesignatedContact.create(DesignatedContact.Type.TECH, techContact));
+    }
+    return builder.build();
+  }
+
   public String getTld() {
     return tld;
   }
@@ -764,7 +678,13 @@ public class DomainContent extends EppResource
     if (includeRegistrant) {
       registrantContact = null;
     }
+    HashSet<DesignatedContact.Type> contactsDiscovered = new HashSet<DesignatedContact.Type>();
     for (DesignatedContact contact : contacts) {
+      checkArgument(
+          !contactsDiscovered.contains(contact.getType()),
+          "Duplicate contact type %s in designated contact set.",
+          contact.getType());
+      contactsDiscovered.add(contact.getType());
       switch (contact.getType()) {
         case BILLING:
           billingContact = contact.getContactKey();
@@ -793,24 +713,6 @@ public class DomainContent extends EppResource
             + " use DomainBase instead");
   }
 
-  /**
-   * Obtains a history id from the given key.
-   *
-   * <p>The key must be a composite key either of the form domain-key/history-key/long-event-key or
-   * EntityGroupRoot/long-event-key (for legacy keys). In the latter case or for a null key returns
-   * a history id of null.
-   */
-  public static Long getHistoryId(VKey<?> key) {
-    if (key == null) {
-      return null;
-    }
-    Key<?> parent = key.getOfyKey().getParent();
-    if (parent == null || parent.getKind().equals("EntityGroupRoot")) {
-      return null;
-    }
-    return parent.getId();
-  }
-
   /** Predicate to determine if a given {@link DesignatedContact} is the registrant. */
   static final Predicate<DesignatedContact> IS_REGISTRANT =
       (DesignatedContact contact) -> DesignatedContact.Type.REGISTRANT.equals(contact.type);
@@ -848,10 +750,6 @@ public class DomainContent extends EppResource
       instance.autorenewEndTime = firstNonNull(getInstance().autorenewEndTime, END_OF_TIME);
 
       checkArgumentNotNull(emptyToNull(instance.fullyQualifiedDomainName), "Missing domainName");
-      if (instance.getRegistrant() == null
-          && instance.allContacts.stream().anyMatch(IS_REGISTRANT)) {
-        throw new IllegalArgumentException("registrant is null but is in allContacts");
-      }
       checkArgumentNotNull(instance.getRegistrant(), "Missing registrant");
       instance.tld = getTldFromDomainName(instance.fullyQualifiedDomainName);
 
@@ -885,13 +783,6 @@ public class DomainContent extends EppResource
     }
 
     public B setRegistrant(VKey<ContactResource> registrant) {
-      // Replace the registrant contact inside allContacts.
-      getInstance().allContacts =
-          union(
-              getInstance().getContacts(),
-              DesignatedContact.create(
-                  DesignatedContact.Type.REGISTRANT, checkArgumentNotNull(registrant)));
-
       // Set the registrant field specifically.
       getInstance().registrantContact = registrant;
       return thisCastToDerived();
@@ -939,13 +830,6 @@ public class DomainContent extends EppResource
     public B setContacts(ImmutableSet<DesignatedContact> contacts) {
       checkArgument(contacts.stream().noneMatch(IS_REGISTRANT), "Registrant cannot be a contact");
 
-      // Replace the non-registrant contacts inside allContacts.
-      getInstance().allContacts =
-          Streams.concat(
-                  nullToEmpty(getInstance().allContacts).stream().filter(IS_REGISTRANT),
-                  contacts.stream())
-              .collect(toImmutableSet());
-
       // Set the individual fields.
       getInstance().setContactFields(contacts, false);
       return thisCastToDerived();
@@ -992,19 +876,19 @@ public class DomainContent extends EppResource
 
     public B setDeletePollMessage(VKey<PollMessage.OneTime> deletePollMessage) {
       getInstance().deletePollMessage = deletePollMessage;
-      getInstance().deletePollMessageHistoryId = getHistoryId(deletePollMessage);
       return thisCastToDerived();
     }
 
     public B setAutorenewBillingEvent(VKey<BillingEvent.Recurring> autorenewBillingEvent) {
       getInstance().autorenewBillingEvent = autorenewBillingEvent;
-      getInstance().autorenewBillingEventHistoryId = getHistoryId(autorenewBillingEvent);
       return thisCastToDerived();
     }
 
-    public B setAutorenewPollMessage(VKey<PollMessage.Autorenew> autorenewPollMessage) {
+    public B setAutorenewPollMessage(
+        @Nullable VKey<PollMessage.Autorenew> autorenewPollMessage,
+        @Nullable Long autorenewPollMessageHistoryId) {
       getInstance().autorenewPollMessage = autorenewPollMessage;
-      getInstance().autorenewPollMessageHistoryId = getHistoryId(autorenewPollMessage);
+      getInstance().autorenewPollMessageHistoryId = autorenewPollMessageHistoryId;
       return thisCastToDerived();
     }
 

core/src/main/java/google/registry/model/domain/DomainHistory.java

@@ -326,23 +326,13 @@ public class DomainHistory extends HistoryEntry {
       this.id = id;
     }
 
-    /**
+    /** Returns the domain repository id. */
-     * Returns the domain repository id.
+    public String getDomainRepoId() {
-     *
-     * <p>This method is private because it is only used by Hibernate.
-     */
-    @SuppressWarnings("unused")
-    private String getDomainRepoId() {
       return domainRepoId;
     }
 
-    /**
+    /** Returns the history revision id. */
-     * Returns the history revision id.
+    public long getId() {
-     *
-     * <p>This method is private because it is only used by Hibernate.
-     */
-    @SuppressWarnings("unused")
-    private long getId() {
       return id;
     }
 

core/src/main/java/google/registry/model/domain/GracePeriod.java

@@ -24,8 +24,6 @@ import google.registry.model.billing.BillingEvent;
 import google.registry.model.billing.BillingEvent.Recurring;
 import google.registry.model.domain.DomainHistory.DomainHistoryId;
 import google.registry.model.domain.rgp.GracePeriodStatus;
-import google.registry.persistence.BillingVKey.BillingEventVKey;
-import google.registry.persistence.BillingVKey.BillingRecurrenceVKey;
 import google.registry.persistence.VKey;
 import javax.annotation.Nullable;
 import javax.persistence.Access;
@@ -78,8 +76,8 @@ public class GracePeriod extends GracePeriodBase {
     instance.domainRepoId = checkArgumentNotNull(domainRepoId);
     instance.expirationTime = checkArgumentNotNull(expirationTime);
     instance.clientId = checkArgumentNotNull(registrarId);
-    instance.billingEventOneTime = BillingEventVKey.create(billingEventOneTime);
+    instance.billingEventOneTime = billingEventOneTime;
-    instance.billingEventRecurring = BillingRecurrenceVKey.create(billingEventRecurring);
+    instance.billingEventRecurring = billingEventRecurring;
     return instance;
   }
 
@@ -126,8 +124,8 @@ public class GracePeriod extends GracePeriodBase {
         history.domainRepoId,
         history.expirationTime,
         history.clientId,
-        history.billingEventOneTime == null ? null : history.billingEventOneTime.createVKey(),
+        history.billingEventOneTime,
-        history.billingEventRecurring == null ? null : history.billingEventRecurring.createVKey(),
+        history.billingEventRecurring,
         history.gracePeriodId);
   }
 

core/src/main/java/google/registry/model/domain/GracePeriodBase.java

@@ -20,8 +20,6 @@ import google.registry.model.ImmutableObject;
 import google.registry.model.UnsafeSerializable;
 import google.registry.model.billing.BillingEvent;
 import google.registry.model.domain.rgp.GracePeriodStatus;
-import google.registry.persistence.BillingVKey.BillingEventVKey;
-import google.registry.persistence.BillingVKey.BillingRecurrenceVKey;
 import google.registry.persistence.VKey;
 import javax.persistence.Access;
 import javax.persistence.AccessType;
@@ -66,7 +64,8 @@ public class GracePeriodBase extends ImmutableObject implements UnsafeSerializab
    */
   // NB: Would @IgnoreSave(IfNull.class), but not allowed for @Embed collections.
   @Access(AccessType.FIELD)
-  BillingEventVKey billingEventOneTime = null;
+  @Column(name = "billing_event_id")
+  VKey<BillingEvent.OneTime> billingEventOneTime = null;
 
   /**
    * The recurring billing event corresponding to the action that triggered this grace period, if
@@ -74,7 +73,8 @@ public class GracePeriodBase extends ImmutableObject implements UnsafeSerializab
    */
   // NB: Would @IgnoreSave(IfNull.class), but not allowed for @Embed collections.
   @Access(AccessType.FIELD)
-  BillingRecurrenceVKey billingEventRecurring = null;
+  @Column(name = "billing_recurrence_id")
+  VKey<BillingEvent.Recurring> billingEventRecurring = null;
 
   public long getGracePeriodId() {
     return gracePeriodId;
@@ -112,7 +112,7 @@ public class GracePeriodBase extends ImmutableObject implements UnsafeSerializab
    * period is not AUTO_RENEW.
    */
   public VKey<BillingEvent.OneTime> getOneTimeBillingEvent() {
-    return billingEventOneTime == null ? null : billingEventOneTime.createVKey();
+    return billingEventOneTime;
   }
 
   /**
@@ -120,6 +120,6 @@ public class GracePeriodBase extends ImmutableObject implements UnsafeSerializab
    * period is AUTO_RENEW.
    */
   public VKey<BillingEvent.Recurring> getRecurringBillingEvent() {
-    return billingEventRecurring == null ? null : billingEventRecurring.createVKey();
+    return billingEventRecurring;
   }
 }

core/src/main/java/google/registry/model/host/HostHistory.java

@@ -85,6 +85,10 @@ public class HostHistory extends HistoryEntry implements UnsafeSerializable {
     return super.getId();
   }
 
+  public HostHistoryId getHostHistoryId() {
+    return new HostHistoryId(getHostRepoId(), getId());
+  }
+
   /**
    * The values of all the fields on the {@link HostBase} object after the action represented by
    * this history object was executed.
@@ -147,8 +151,7 @@ public class HostHistory extends HistoryEntry implements UnsafeSerializable {
      *
      * <p>This method is private because it is only used by Hibernate.
      */
-    @SuppressWarnings("unused")
+    public String getHostRepoId() {
-    private String getHostRepoId() {
       return hostRepoId;
     }
 
@@ -157,8 +160,7 @@ public class HostHistory extends HistoryEntry implements UnsafeSerializable {
      *
      * <p>This method is private because it is only used by Hibernate.
      */
-    @SuppressWarnings("unused")
+    public long getId() {
-    private long getId() {
       return id;
     }
 

core/src/main/java/google/registry/model/poll/PollMessage.java

@@ -14,10 +14,8 @@
 
 package google.registry.model.poll;
 
-import static com.google.common.collect.ImmutableList.toImmutableList;
+import static com.google.common.base.Preconditions.checkArgument;
-import static google.registry.util.CollectionUtils.forceEmptyToNull;
+import static com.google.common.base.Preconditions.checkState;
-import static google.registry.util.CollectionUtils.isNullOrEmpty;
-import static google.registry.util.CollectionUtils.nullToEmpty;
 import static google.registry.util.DateTimeUtils.END_OF_TIME;
 import static google.registry.util.PreconditionsUtils.checkArgumentNotNull;
 
@@ -28,18 +26,22 @@ import com.googlecode.objectify.annotation.EntitySubclass;
 import com.googlecode.objectify.annotation.Id;
 import com.googlecode.objectify.annotation.Ignore;
 import com.googlecode.objectify.annotation.Index;
-import com.googlecode.objectify.annotation.OnLoad;
-import com.googlecode.objectify.annotation.Parent;
 import google.registry.model.Buildable;
 import google.registry.model.EppResource;
 import google.registry.model.ImmutableObject;
 import google.registry.model.UnsafeSerializable;
 import google.registry.model.annotations.ExternalMessagingName;
 import google.registry.model.annotations.ReportedOn;
+import google.registry.model.contact.ContactHistory;
+import google.registry.model.contact.ContactHistory.ContactHistoryId;
 import google.registry.model.contact.ContactResource;
 import google.registry.model.domain.DomainBase;
+import google.registry.model.domain.DomainHistory;
+import google.registry.model.domain.DomainHistory.DomainHistoryId;
 import google.registry.model.domain.DomainRenewData;
 import google.registry.model.eppoutput.EppResponse.ResponseData;
+import google.registry.model.host.HostHistory;
+import google.registry.model.host.HostHistory.HostHistoryId;
 import google.registry.model.host.HostResource;
 import google.registry.model.poll.PendingActionNotificationResponse.ContactPendingActionNotificationResponse;
 import google.registry.model.poll.PendingActionNotificationResponse.DomainPendingActionNotificationResponse;
@@ -51,7 +53,7 @@ import google.registry.model.transfer.TransferResponse.ContactTransferResponse;
 import google.registry.model.transfer.TransferResponse.DomainTransferResponse;
 import google.registry.persistence.VKey;
 import google.registry.persistence.WithLongVKey;
-import java.util.List;
+import google.registry.util.NullIgnoringCollectionBuilder;
 import java.util.Optional;
 import javax.annotation.Nullable;
 import javax.persistence.AttributeOverride;
@@ -63,7 +65,6 @@ import javax.persistence.Embedded;
 import javax.persistence.Inheritance;
 import javax.persistence.InheritanceType;
 import javax.persistence.PostLoad;
-import javax.persistence.Transient;
 import org.joda.time.DateTime;
 
 /**
@@ -100,14 +101,54 @@ import org.joda.time.DateTime;
 public abstract class PollMessage extends ImmutableObject
     implements Buildable, TransferServerApproveEntity, UnsafeSerializable {
 
+  /** Indicates the type of entity the poll message is for. */
+  public enum Type {
+    DOMAIN(1L, DomainBase.class),
+    CONTACT(2L, ContactResource.class),
+    HOST(3L, HostResource.class);
+
+    private final long id;
+    private final Class<?> clazz;
+
+    Type(long id, Class<?> clazz) {
+      this.id = id;
+      this.clazz = clazz;
+    }
+
+    /**
+     * Returns a numeric id for the enum, which is used as part of an externally published string
+     * key for the message.
+     */
+    public long getId() {
+      return id;
+    }
+
+    /** Returns the class of the underlying resource for the poll message type. */
+    public Class<?> getResourceClass() {
+      return clazz;
+    }
+
+    /**
+     * Returns the type specified by the identifer, {@code Optional.empty()} if the id is out of
+     * range.
+     */
+    public static Optional<Type> fromId(long id) {
+      for (Type val : values()) {
+        if (val.id == id) {
+          return Optional.of(val);
+        }
+      }
+
+      return Optional.empty();
+    }
+  }
+
   /** Entity id. */
   @Id
   @javax.persistence.Id
   @Column(name = "poll_message_id")
   Long id;
 
-  @Parent @DoNotHydrate @Transient Key<? extends HistoryEntry> parent;
-
   /** The registrar that this poll message will be delivered to. */
   @Index
   @Column(name = "registrar_id", nullable = false)
@@ -122,6 +163,8 @@ public abstract class PollMessage extends ImmutableObject
   @Column(name = "message")
   String msg;
 
+  // TODO(b/456803336): Replace these fields with {Domain,Contact,Host}HistoryId objects.
+
   @Ignore String domainRepoId;
 
   @Ignore String contactRepoId;
@@ -134,10 +177,6 @@ public abstract class PollMessage extends ImmutableObject
 
   @Ignore Long hostHistoryRevisionId;
 
-  public Key<? extends HistoryEntry> getParentKey() {
-    return parent;
-  }
-
   public Long getId() {
     return id;
   }
@@ -154,36 +193,59 @@ public abstract class PollMessage extends ImmutableObject
     return msg;
   }
 
+  /**
+   * Returns the domain repo id.
+   *
+   * <p>This may only be used on a Domain poll event.
+   */
+  public String getDomainRepoId() {
+    checkArgument(getType() == Type.DOMAIN);
+    return domainRepoId;
+  }
+
+  /**
+   * Returns the contact repo id.
+   *
+   * <p>This may only be used on a ContactResource poll event.
+   */
+  public String getContactRepoId() {
+    checkArgument(getType() == Type.CONTACT);
+    return contactRepoId;
+  }
+
+  /**
+   * Returns the host repo id.
+   *
+   * <p>This may only be used on a HostResource poll event.
+   */
+  public String getHostRepoId() {
+    checkArgument(getType() == Type.DOMAIN);
+    return hostRepoId;
+  }
+
+  /**
+   * Gets the name of the underlying resource that the PollMessage is for, regardless of the type of
+   * the resource.
+   */
+  public String getResourceName() {
+    return domainRepoId != null
+        ? domainRepoId
+        : (contactRepoId != null ? contactRepoId : hostRepoId);
+  }
+
+  /** Gets the underlying history revision id, regardless of the type of the resource. */
+  public Long getHistoryRevisionId() {
+    return domainHistoryRevisionId != null
+        ? domainHistoryRevisionId
+        : (contactHistoryRevisionId != null ? contactHistoryRevisionId : hostHistoryRevisionId);
+  }
+
+  public Type getType() {
+    return domainRepoId != null ? Type.DOMAIN : (contactRepoId != null ? Type.CONTACT : Type.HOST);
+  }
+
   public abstract ImmutableList<ResponseData> getResponseData();
 
-  @PostLoad
-  void postLoad() {
-    if (domainRepoId != null) {
-      parent =
-          Key.create(
-              Key.create(DomainBase.class, domainRepoId),
-              HistoryEntry.class,
-              domainHistoryRevisionId);
-    } else if (contactRepoId != null) {
-      parent =
-          Key.create(
-              Key.create(ContactResource.class, contactRepoId),
-              HistoryEntry.class,
-              contactHistoryRevisionId);
-    } else if (hostHistoryRevisionId != null) {
-      parent =
-          Key.create(
-              Key.create(HostResource.class, hostRepoId),
-              HistoryEntry.class,
-              hostHistoryRevisionId);
-    }
-  }
-
-  @OnLoad
-  void onLoad() {
-    setSqlForeignKeys(this);
-  }
-
   @Override
   public abstract VKey<? extends PollMessage> createVKey();
 
@@ -234,46 +296,77 @@ public abstract class PollMessage extends ImmutableObject
       return thisCastToDerived();
     }
 
-    public B setParent(HistoryEntry parent) {
+    public B setDomainHistoryId(DomainHistoryId historyId) {
-      getInstance().parent = Key.create(parent);
+      getInstance().domainRepoId = historyId.getDomainRepoId();
+      getInstance().domainHistoryRevisionId = historyId.getId();
       return thisCastToDerived();
     }
 
-    public B setParentKey(Key<? extends HistoryEntry> parentKey) {
+    public B setContactHistoryId(ContactHistoryId historyId) {
-      getInstance().parent = parentKey;
+      getInstance().contactRepoId = historyId.getContactRepoId();
+      getInstance().contactHistoryRevisionId = historyId.getId();
       return thisCastToDerived();
     }
 
+    public B setHostHistoryId(HostHistoryId historyId) {
+      getInstance().hostRepoId = historyId.getHostRepoId();
+      getInstance().hostHistoryRevisionId = historyId.getId();
+      return thisCastToDerived();
+    }
+
+    public B setHistoryEntry(HistoryEntry history) {
+      // Set the appropriate field based on the history entry type.
+      if (history instanceof DomainHistory) {
+        return setDomainHistoryId(((DomainHistory) history).getDomainHistoryId());
+      } else if (history instanceof ContactHistory) {
+        return setContactHistoryId(((ContactHistory) history).getContactHistoryId());
+      } else if (history instanceof HostHistory) {
+        return setHostHistoryId(((HostHistory) history).getHostHistoryId());
+      }
+      return thisCastToDerived();
+    }
+
+    /**
+     * Given an array containing pairs of objects, verifies that both members of exactly one of the
+     * pairs is non-null.
+     */
+    private boolean exactlyOnePairNonNull(Object... pairs) {
+      int count = 0;
+      checkArgument(pairs.length % 2 == 0, "Odd number of arguments provided.");
+      for (int i = 0; i < pairs.length; i += 2) {
+        // Add the number of non-null elements of each pair, after which the count should either be
+        // zero (a non-null pair hasn't been found yet) or two (exactly one non-null pair has been
+        // found).
+        count += (pairs[i] != null ? 1 : 0) + (pairs[i + 1] != null ? 1 : 0);
+        if (count != 0 && count != 2) {
+          return false;
+        }
+      }
+
+      // Verify that we've found a non-null pair.
+      return count == 2;
+    }
+
     @Override
     public T build() {
       T instance = getInstance();
       checkArgumentNotNull(instance.clientId, "clientId must be specified");
       checkArgumentNotNull(instance.eventTime, "eventTime must be specified");
-      checkArgumentNotNull(instance.parent, "parent must be specified");
+      checkState(
-      checkArgumentNotNull(instance.parent.getParent(), "parent.getParent() must be specified");
+          exactlyOnePairNonNull(
-      setSqlForeignKeys(instance);
+              instance.domainRepoId,
+              instance.domainHistoryRevisionId,
+              instance.contactRepoId,
+              instance.contactHistoryRevisionId,
+              instance.hostRepoId,
+              instance.hostHistoryRevisionId),
+          "the repo id and history revision id must be defined for exactly one of domain, "
+              + "contact or host: "
+              + instance);
       return super.build();
     }
   }
 
-  private static void setSqlForeignKeys(PollMessage pollMessage) {
-    String grandparentKind = pollMessage.parent.getParent().getKind();
-    String repoId = pollMessage.parent.getParent().getName();
-    long historyRevisionId = pollMessage.parent.getId();
-    if (Key.getKind(DomainBase.class).equals(grandparentKind)) {
-      pollMessage.domainRepoId = repoId;
-      pollMessage.domainHistoryRevisionId = historyRevisionId;
-    } else if (Key.getKind(ContactResource.class).equals(grandparentKind)) {
-      pollMessage.contactRepoId = repoId;
-      pollMessage.contactHistoryRevisionId = historyRevisionId;
-    } else if (Key.getKind(HostResource.class).equals(grandparentKind)) {
-      pollMessage.hostRepoId = repoId;
-      pollMessage.hostHistoryRevisionId = historyRevisionId;
-    } else {
-      throw new IllegalArgumentException("Unknown grandparent kind: " + grandparentKind);
-    }
-  }
-
   /**
    * A one-time poll message.
    *
@@ -285,20 +378,6 @@ public abstract class PollMessage extends ImmutableObject
   @WithLongVKey(compositeKey = true)
   public static class OneTime extends PollMessage {
 
-    // Response data. Objectify cannot persist a base class type, so we must have a separate field
-    // to hold every possible derived type of ResponseData that we might store.
-    @Transient
-    List<ContactPendingActionNotificationResponse> contactPendingActionNotificationResponses;
-
-    @Transient List<ContactTransferResponse> contactTransferResponses;
-
-    @Transient @ImmutableObject.DoNotCompare
-    List<DomainPendingActionNotificationResponse> domainPendingActionNotificationResponses;
-
-    @Transient @ImmutableObject.DoNotCompare List<DomainTransferResponse> domainTransferResponses;
-
-    @Transient List<HostPendingActionNotificationResponse> hostPendingActionNotificationResponses;
-
     @Ignore
     @Embedded
     @AttributeOverrides({
@@ -379,78 +458,38 @@ public abstract class PollMessage extends ImmutableObject
 
     @Override
     public ImmutableList<ResponseData> getResponseData() {
-      return new ImmutableList.Builder<ResponseData>()
+      return NullIgnoringCollectionBuilder.create(new ImmutableList.Builder<ResponseData>())
-          .addAll(nullToEmpty(contactPendingActionNotificationResponses))
+          .add(pendingActionNotificationResponse)
-          .addAll(nullToEmpty(contactTransferResponses))
+          .add(transferResponse)
-          .addAll(nullToEmpty(domainPendingActionNotificationResponses))
+          .getBuilder()
-          .addAll(nullToEmpty(domainTransferResponses))
-          .addAll(nullToEmpty(hostPendingActionNotificationResponses))
           .build();
     }
 
-    @Override
-    @OnLoad
-    void onLoad() {
-      super.onLoad();
-      // Take the Objectify-specific fields and map them to the SQL-specific fields, if applicable
-      if (!isNullOrEmpty(contactPendingActionNotificationResponses)) {
-        contactId = contactPendingActionNotificationResponses.get(0).getId().value;
-        pendingActionNotificationResponse = contactPendingActionNotificationResponses.get(0);
-      }
-      if (!isNullOrEmpty(hostPendingActionNotificationResponses)) {
-        hostId = hostPendingActionNotificationResponses.get(0).nameOrId.value;
-        pendingActionNotificationResponse = hostPendingActionNotificationResponses.get(0);
-      }
-      if (!isNullOrEmpty(contactTransferResponses)) {
-        contactId = contactTransferResponses.get(0).getContactId();
-        transferResponse = contactTransferResponses.get(0);
-      }
-      if (!isNullOrEmpty(domainPendingActionNotificationResponses)) {
-        pendingActionNotificationResponse = domainPendingActionNotificationResponses.get(0);
-        fullyQualifiedDomainName = pendingActionNotificationResponse.nameOrId.value;
-      }
-      if (!isNullOrEmpty(domainTransferResponses)) {
-        fullyQualifiedDomainName = domainTransferResponses.get(0).getFullyQualifiedDomainName();
-        transferResponse = domainTransferResponses.get(0);
-        extendedRegistrationExpirationTime =
-            domainTransferResponses.get(0).getExtendedRegistrationExpirationTime();
-      }
-    }
-
-    @Override
     @PostLoad
     void postLoad() {
-      super.postLoad();
-      // Take the SQL-specific fields and map them to the Objectify-specific fields, if applicable
       if (pendingActionNotificationResponse != null) {
+        // Promote the pending action notification response to its specialized type.
         if (contactId != null) {
-          ContactPendingActionNotificationResponse contactPendingResponse =
+          pendingActionNotificationResponse =
               ContactPendingActionNotificationResponse.create(
                   pendingActionNotificationResponse.nameOrId.value,
                   pendingActionNotificationResponse.getActionResult(),
                   pendingActionNotificationResponse.getTrid(),
                   pendingActionNotificationResponse.processedDate);
-          pendingActionNotificationResponse = contactPendingResponse;
-          contactPendingActionNotificationResponses = ImmutableList.of(contactPendingResponse);
         } else if (fullyQualifiedDomainName != null) {
-          DomainPendingActionNotificationResponse domainPendingResponse =
+          pendingActionNotificationResponse =
               DomainPendingActionNotificationResponse.create(
                   pendingActionNotificationResponse.nameOrId.value,
                   pendingActionNotificationResponse.getActionResult(),
                   pendingActionNotificationResponse.getTrid(),
                   pendingActionNotificationResponse.processedDate);
-          pendingActionNotificationResponse = domainPendingResponse;
-          domainPendingActionNotificationResponses = ImmutableList.of(domainPendingResponse);
         } else if (hostId != null) {
-          HostPendingActionNotificationResponse hostPendingActionNotificationResponse =
+          pendingActionNotificationResponse =
               HostPendingActionNotificationResponse.create(
                   pendingActionNotificationResponse.nameOrId.value,
                   pendingActionNotificationResponse.getActionResult(),
                   pendingActionNotificationResponse.getTrid(),
                   pendingActionNotificationResponse.processedDate);
-          pendingActionNotificationResponse = hostPendingActionNotificationResponse;
-          hostPendingActionNotificationResponses =
-              ImmutableList.of(hostPendingActionNotificationResponse);
         }
       }
       if (transferResponse != null) {
@@ -467,7 +506,6 @@ public abstract class PollMessage extends ImmutableObject
                   .setPendingTransferExpirationTime(
                       transferResponse.getPendingTransferExpirationTime())
                   .build();
-          contactTransferResponses = ImmutableList.of((ContactTransferResponse) transferResponse);
         } else if (fullyQualifiedDomainName != null) {
           transferResponse =
               new DomainTransferResponse.Builder()
@@ -480,7 +518,6 @@ public abstract class PollMessage extends ImmutableObject
                       transferResponse.getPendingTransferExpirationTime())
                   .setExtendedRegistrationExpirationTime(extendedRegistrationExpirationTime)
                   .build();
-          domainTransferResponses = ImmutableList.of((DomainTransferResponse) transferResponse);
         }
       }
     }
@@ -497,66 +534,52 @@ public abstract class PollMessage extends ImmutableObject
 
       public Builder setResponseData(ImmutableList<? extends ResponseData> responseData) {
         OneTime instance = getInstance();
-        instance.contactPendingActionNotificationResponses =
+        // Note: In its current form, the code will basically just ignore everything but the first
-            forceEmptyToNull(
+        // PendingActionNotificationResponse and TransferResponse in responseData, and will override
-                responseData.stream()
+        // any identifier fields (e.g. contactId, fullyQualifiedDomainName) obtained from the
-                    .filter(ContactPendingActionNotificationResponse.class::isInstance)
+        // PendingActionNotificationResponse if a TransferResponse is found with different values
-                    .map(ContactPendingActionNotificationResponse.class::cast)
+        // for those fields.  It is not clear what the constraints should be on this data or
-                    .collect(toImmutableList()));
+        // whether we should enforce them here, though historically we have not, so the current
+        // implementation doesn't.
 
-        instance.contactTransferResponses =
+        // Extract the first PendingActionNotificationResponse element from the list if there is
-            forceEmptyToNull(
+        // one.
-                responseData.stream()
+        instance.pendingActionNotificationResponse =
-                    .filter(ContactTransferResponse.class::isInstance)
+            responseData.stream()
-                    .map(ContactTransferResponse.class::cast)
+                .filter(PendingActionNotificationResponse.class::isInstance)
-                    .collect(toImmutableList()));
+                .map(PendingActionNotificationResponse.class::cast)
+                .findFirst()
+                .orElse(null);
 
-        instance.domainPendingActionNotificationResponses =
+        // Set identifier fields based on the type of the notification response.
-            forceEmptyToNull(
+        if (instance.pendingActionNotificationResponse
-                responseData.stream()
+            instanceof ContactPendingActionNotificationResponse) {
-                    .filter(DomainPendingActionNotificationResponse.class::isInstance)
+          instance.contactId = instance.pendingActionNotificationResponse.nameOrId.value;
-                    .map(DomainPendingActionNotificationResponse.class::cast)
+        } else if (instance.pendingActionNotificationResponse
-                    .collect(toImmutableList()));
+            instanceof DomainPendingActionNotificationResponse) {
-        instance.domainTransferResponses =
-            forceEmptyToNull(
-                responseData.stream()
-                    .filter(DomainTransferResponse.class::isInstance)
-                    .map(DomainTransferResponse.class::cast)
-                    .collect(toImmutableList()));
-
-        instance.hostPendingActionNotificationResponses =
-            forceEmptyToNull(
-                responseData.stream()
-                    .filter(HostPendingActionNotificationResponse.class::isInstance)
-                    .map(HostPendingActionNotificationResponse.class::cast)
-                    .collect(toImmutableList()));
-
-        // Set the generic pending-action field as appropriate
-        if (instance.contactPendingActionNotificationResponses != null) {
-          instance.pendingActionNotificationResponse =
-              instance.contactPendingActionNotificationResponses.get(0);
-          instance.contactId =
-              instance.contactPendingActionNotificationResponses.get(0).nameOrId.value;
-        } else if (instance.domainPendingActionNotificationResponses != null) {
-          instance.pendingActionNotificationResponse =
-              instance.domainPendingActionNotificationResponses.get(0);
           instance.fullyQualifiedDomainName =
-              instance.domainPendingActionNotificationResponses.get(0).nameOrId.value;
+              instance.pendingActionNotificationResponse.nameOrId.value;
-        } else if (instance.hostPendingActionNotificationResponses != null) {
+        } else if (instance.pendingActionNotificationResponse
-          instance.pendingActionNotificationResponse =
+            instanceof HostPendingActionNotificationResponse) {
-              instance.hostPendingActionNotificationResponses.get(0);
+          instance.hostId = instance.pendingActionNotificationResponse.nameOrId.value;
-          instance.hostId = instance.hostPendingActionNotificationResponses.get(0).nameOrId.value;
         }
-        // Set the generic transfer response field as appropriate
+
-        if (instance.contactTransferResponses != null) {
+        // Extract the first TransferResponse from the list.
-          instance.contactId = getInstance().contactTransferResponses.get(0).getContactId();
+        instance.transferResponse =
-          instance.transferResponse = getInstance().contactTransferResponses.get(0);
+            responseData.stream()
-        } else if (instance.domainTransferResponses != null) {
+                .filter(TransferResponse.class::isInstance)
-          instance.fullyQualifiedDomainName =
+                .map(TransferResponse.class::cast)
-              instance.domainTransferResponses.get(0).getFullyQualifiedDomainName();
+                .findFirst()
-          instance.transferResponse = getInstance().domainTransferResponses.get(0);
+                .orElse(null);
+
+        // Set the identifier according to the TransferResponse type.
+        if (instance.transferResponse instanceof ContactTransferResponse) {
+          instance.contactId = ((ContactTransferResponse) instance.transferResponse).getContactId();
+        } else if (instance.transferResponse instanceof DomainTransferResponse) {
+          DomainTransferResponse response = (DomainTransferResponse) instance.transferResponse;
+          instance.fullyQualifiedDomainName = response.getFullyQualifiedDomainName();
           instance.extendedRegistrationExpirationTime =
-              instance.domainTransferResponses.get(0).getExtendedRegistrationExpirationTime();
+              response.getExtendedRegistrationExpirationTime();
         }
         return this;
       }

core/src/main/java/google/registry/model/poll/PollMessageExternalKeyConverter.java

@@ -14,19 +14,12 @@
 
 package google.registry.model.poll;
 
-import static com.google.common.collect.ImmutableMap.toImmutableMap;
 
 import com.google.common.base.Splitter;
-import com.google.common.collect.ImmutableMap;
 import com.googlecode.objectify.Key;
-import google.registry.model.EppResource;
-import google.registry.model.contact.ContactResource;
-import google.registry.model.domain.DomainBase;
-import google.registry.model.host.HostResource;
 import google.registry.model.reporting.HistoryEntry;
 import google.registry.persistence.VKey;
 import java.util.List;
-import java.util.Map;
 
 /**
  * A converter between external key strings for {@link PollMessage}s (i.e. what registrars use to
@@ -50,28 +43,13 @@ public class PollMessageExternalKeyConverter {
   /** An exception thrown when an external key cannot be parsed. */
   public static class PollMessageExternalKeyParseException extends RuntimeException {}
 
-  /** Maps that detail the correspondence between EppResource classes and external IDs. */
-  private static final ImmutableMap<Long, Class<? extends EppResource>> ID_TO_CLASS_MAP =
-      ImmutableMap.of(
-          1L, DomainBase.class,
-          2L, ContactResource.class,
-          3L, HostResource.class);
-
-  private static final ImmutableMap<String, Long> KEY_KIND_TO_ID_MAP =
-      ID_TO_CLASS_MAP.entrySet().stream()
-          .collect(toImmutableMap(entry -> entry.getValue().getSimpleName(), Map.Entry::getKey));
-
   /** Returns an external poll message ID for the given poll message. */
   public static String makePollMessageExternalId(PollMessage pollMessage) {
-    @SuppressWarnings("unchecked")
-    Key<EppResource> ancestorResource =
-        (Key<EppResource>) (Key<?>) pollMessage.getParentKey().getParent();
-    long externalKeyClassId = KEY_KIND_TO_ID_MAP.get(ancestorResource.getKind());
     return String.format(
         "%d-%s-%d-%d-%d",
-        externalKeyClassId,
+        pollMessage.getType().getId(),
-        ancestorResource.getName(),
+        pollMessage.getResourceName(),
-        pollMessage.getParentKey().getId(),
+        pollMessage.getHistoryRevisionId(),
         pollMessage.getId(),
         pollMessage.getEventTime().getYear());
   }
@@ -92,10 +70,10 @@ public class PollMessageExternalKeyConverter {
       throw new PollMessageExternalKeyParseException();
     }
     try {
-      Class<?> resourceClazz = ID_TO_CLASS_MAP.get(Long.parseLong(idComponents.get(0)));
+      Class<?> resourceClazz =
-      if (resourceClazz == null) {
+          PollMessage.Type.fromId(Long.parseLong(idComponents.get(0)))
-        throw new PollMessageExternalKeyParseException();
+              .orElseThrow(() -> new PollMessageExternalKeyParseException())
-      }
+              .getResourceClass();
       return VKey.from(
           Key.create(
               Key.create(
@@ -115,4 +93,3 @@ public class PollMessageExternalKeyConverter {
 
   private PollMessageExternalKeyConverter() {}
 }
-

core/src/main/java/google/registry/model/transfer/DomainTransferData.java

@@ -14,25 +14,20 @@
 
 package google.registry.model.transfer;
 
-import static google.registry.util.CollectionUtils.forceEmptyToNull;
 import static google.registry.util.CollectionUtils.isNullOrEmpty;
 
-import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableSet;
-import com.googlecode.objectify.Key;
-import com.googlecode.objectify.annotation.AlsoLoad;
 import com.googlecode.objectify.annotation.Embed;
 import com.googlecode.objectify.annotation.Ignore;
 import com.googlecode.objectify.annotation.IgnoreSave;
-import com.googlecode.objectify.annotation.OnLoad;
 import com.googlecode.objectify.annotation.Unindex;
 import com.googlecode.objectify.condition.IfNull;
 import google.registry.model.billing.BillingEvent;
-import google.registry.model.domain.DomainBase;
 import google.registry.model.domain.Period;
 import google.registry.model.domain.Period.Unit;
 import google.registry.model.poll.PollMessage;
 import google.registry.persistence.VKey;
+import google.registry.util.NullIgnoringCollectionBuilder;
 import java.util.Set;
 import javax.annotation.Nullable;
 import javax.persistence.AttributeOverride;
@@ -40,7 +35,6 @@ import javax.persistence.AttributeOverrides;
 import javax.persistence.Column;
 import javax.persistence.Embeddable;
 import javax.persistence.Embedded;
-import javax.persistence.PostLoad;
 import org.joda.time.DateTime;
 
 /** Transfer data for domain. */
@@ -85,10 +79,6 @@ public class DomainTransferData extends TransferData<DomainTransferData.Builder>
   @Column(name = "transfer_billing_cancellation_id")
   public VKey<BillingEvent.Cancellation> billingCancellationId;
 
-  @Ignore
-  @Column(name = "transfer_billing_cancellation_history_id")
-  Long billingCancellationHistoryId;
-
   /**
    * The regular one-time billing event that will be charged for a server-approved transfer.
    *
@@ -99,10 +89,6 @@ public class DomainTransferData extends TransferData<DomainTransferData.Builder>
   @Column(name = "transfer_billing_event_id")
   VKey<BillingEvent.OneTime> serverApproveBillingEvent;
 
-  @Ignore
-  @Column(name = "transfer_billing_event_history_id")
-  Long serverApproveBillingEventHistoryId;
-
   /**
    * The autorenew billing event that should be associated with this resource after the transfer.
    *
@@ -113,10 +99,6 @@ public class DomainTransferData extends TransferData<DomainTransferData.Builder>
   @Column(name = "transfer_billing_recurrence_id")
   VKey<BillingEvent.Recurring> serverApproveAutorenewEvent;
 
-  @Ignore
-  @Column(name = "transfer_billing_recurrence_history_id")
-  Long serverApproveAutorenewEventHistoryId;
-
   /**
    * The autorenew poll message that should be associated with this resource after the transfer.
    *
@@ -127,6 +109,10 @@ public class DomainTransferData extends TransferData<DomainTransferData.Builder>
   @Column(name = "transfer_autorenew_poll_message_id")
   VKey<PollMessage.Autorenew> serverApproveAutorenewPollMessage;
 
+  /**
+   * Autorenew history, which we need to preserve because it's often used in contexts where we
+   * haven't loaded the autorenew object.
+   */
   @Ignore
   @Column(name = "transfer_autorenew_poll_message_history_id")
   Long serverApproveAutorenewPollMessageHistoryId;
@@ -136,36 +122,6 @@ public class DomainTransferData extends TransferData<DomainTransferData.Builder>
     return super.copyConstantFieldsToBuilder().setTransferPeriod(this.transferPeriod);
   }
 
-  /**
-   * Restores the set of ofy keys after loading from SQL using the specified {@code rootKey}.
-   *
-   * <p>This is for use by DomainBase/DomainHistory PostLoad methods ONLY.
-   */
-  public void restoreOfyKeys(Key<DomainBase> rootKey) {
-    serverApproveBillingEvent =
-        DomainBase.restoreOfyFrom(
-            rootKey, serverApproveBillingEvent, serverApproveBillingEventHistoryId);
-    serverApproveAutorenewEvent =
-        DomainBase.restoreOfyFrom(
-            rootKey, serverApproveAutorenewEvent, serverApproveAutorenewEventHistoryId);
-    serverApproveAutorenewPollMessage =
-        DomainBase.restoreOfyFrom(
-            rootKey, serverApproveAutorenewPollMessage, serverApproveAutorenewPollMessageHistoryId);
-    billingCancellationId =
-        DomainBase.restoreOfyFrom(rootKey, billingCancellationId, billingCancellationHistoryId);
-
-    // Reconstruct server approve entities.  We currently have to call postLoad() a _second_ time
-    // if any of the billing objects have been reconstituted, as they are part of that set.
-    // TODO(b/183010623): Normalize the approaches to VKey reconstitution for the TransferData
-    // hierarchy (the logic currently lives either in PostLoad or here, depending on the key).
-    if (billingCancellationId != null
-        || serverApproveBillingEvent != null
-        || serverApproveAutorenewEvent != null) {
-      serverApproveEntities = null;
-      postLoad();
-    }
-  }
-
   /**
    * Fix the VKey "kind" for the PollMessage keys.
    *
@@ -176,30 +132,6 @@ public class DomainTransferData extends TransferData<DomainTransferData.Builder>
         PollMessage.Autorenew.convertVKey(serverApproveAutorenewPollMessage);
   }
 
-  @SuppressWarnings("unused") // For Hibernate.
-  private void loadServerApproveBillingEventHistoryId(
-      @AlsoLoad("serverApproveBillingEvent") VKey<BillingEvent.OneTime> val) {
-    serverApproveBillingEventHistoryId = DomainBase.getHistoryId(val);
-  }
-
-  @SuppressWarnings("unused") // For Hibernate.
-  private void loadServerApproveAutorenewEventHistoryId(
-      @AlsoLoad("serverApproveAutorenewEvent") VKey<BillingEvent.Recurring> val) {
-    serverApproveAutorenewEventHistoryId = DomainBase.getHistoryId(val);
-  }
-
-  @SuppressWarnings("unused") // For Hibernate.
-  private void loadServerApproveAutorenewPollMessageHistoryId(
-      @AlsoLoad("serverApproveAutorenewPollMessage") VKey<PollMessage.Autorenew> val) {
-    serverApproveAutorenewPollMessageHistoryId = DomainBase.getHistoryId(val);
-  }
-
-  @SuppressWarnings("unused") // For Hibernate.
-  private void billingCancellationHistoryId(
-      @AlsoLoad("billingCancellationHistoryId") VKey<BillingEvent.Cancellation> val) {
-    billingCancellationHistoryId = DomainBase.getHistoryId(val);
-  }
-
   public Period getTransferPeriod() {
     return transferPeriod;
   }
@@ -214,64 +146,32 @@ public class DomainTransferData extends TransferData<DomainTransferData.Builder>
     return serverApproveBillingEvent;
   }
 
-  @VisibleForTesting
-  @Nullable
-  public Long getServerApproveBillingEventHistoryId() {
-    return serverApproveBillingEventHistoryId;
-  }
-
   @Nullable
   public VKey<BillingEvent.Recurring> getServerApproveAutorenewEvent() {
     return serverApproveAutorenewEvent;
   }
 
-  @VisibleForTesting
-  @Nullable
-  public Long getServerApproveAutorenewEventHistoryId() {
-    return serverApproveAutorenewEventHistoryId;
-  }
-
   @Nullable
   public VKey<PollMessage.Autorenew> getServerApproveAutorenewPollMessage() {
     return serverApproveAutorenewPollMessage;
   }
 
-  @VisibleForTesting
   @Nullable
   public Long getServerApproveAutorenewPollMessageHistoryId() {
     return serverApproveAutorenewPollMessageHistoryId;
   }
 
-  @OnLoad
   @Override
-  void onLoad(
+  public ImmutableSet<VKey<? extends TransferServerApproveEntity>> getServerApproveEntities() {
-      @AlsoLoad("serverApproveEntities")
+    ImmutableSet.Builder<VKey<? extends TransferServerApproveEntity>> builder =
-          Set<VKey<? extends TransferServerApproveEntity>> serverApproveEntities) {
-    super.onLoad(serverApproveEntities);
-    mapBillingCancellationEntityToField(serverApproveEntities, this);
-  }
-
-  @PostLoad
-  @Override
-  void postLoad() {
-    super.postLoad();
-    // The superclass's serverApproveEntities should include the billing events if present
-    ImmutableSet.Builder<VKey<? extends TransferServerApproveEntity>> serverApproveEntitiesBuilder =
         new ImmutableSet.Builder<>();
-    if (serverApproveEntities != null) {
+    builder.addAll(super.getServerApproveEntities());
-      serverApproveEntitiesBuilder.addAll(serverApproveEntities);
+    return NullIgnoringCollectionBuilder.create(builder)
-    }
+        .add(serverApproveBillingEvent)
-    if (serverApproveBillingEvent != null) {
+        .add(serverApproveAutorenewEvent)
-      serverApproveEntitiesBuilder.add(serverApproveBillingEvent);
+        .add(billingCancellationId)
-    }
+        .getBuilder()
-    if (serverApproveAutorenewEvent != null) {
+        .build();
-      serverApproveEntitiesBuilder.add(serverApproveAutorenewEvent);
-    }
-    if (billingCancellationId != null) {
-      serverApproveEntitiesBuilder.add(billingCancellationId);
-    }
-    serverApproveEntities = forceEmptyToNull(serverApproveEntitiesBuilder.build());
-    hashCode = null; // reset the hash code since we may have changed the entities
   }
 
   @Override
@@ -291,7 +191,6 @@ public class DomainTransferData extends TransferData<DomainTransferData.Builder>
       DomainTransferData domainTransferData) {
     if (isNullOrEmpty(serverApproveEntities)) {
       domainTransferData.billingCancellationId = null;
-      domainTransferData.billingCancellationHistoryId = null;
     } else {
       domainTransferData.billingCancellationId =
           (VKey<BillingEvent.Cancellation>)
@@ -299,10 +198,6 @@ public class DomainTransferData extends TransferData<DomainTransferData.Builder>
                   .filter(k -> k.getKind().equals(BillingEvent.Cancellation.class))
                   .findFirst()
                   .orElse(null);
-      domainTransferData.billingCancellationHistoryId =
-          domainTransferData.billingCancellationId != null
-              ? DomainBase.getHistoryId(domainTransferData.billingCancellationId)
-              : null;
     }
   }
 
@@ -315,12 +210,6 @@ public class DomainTransferData extends TransferData<DomainTransferData.Builder>
       super(instance);
     }
 
-    @Override
-    public DomainTransferData build() {
-      mapBillingCancellationEntityToField(getInstance().serverApproveEntities, getInstance());
-      return super.build();
-    }
-
     public Builder setTransferPeriod(Period transferPeriod) {
       getInstance().transferPeriod = transferPeriod;
       return this;
@@ -335,24 +224,28 @@ public class DomainTransferData extends TransferData<DomainTransferData.Builder>
     public Builder setServerApproveBillingEvent(
         VKey<BillingEvent.OneTime> serverApproveBillingEvent) {
       getInstance().serverApproveBillingEvent = serverApproveBillingEvent;
-      getInstance().serverApproveBillingEventHistoryId =
-          DomainBase.getHistoryId(serverApproveBillingEvent);
       return this;
     }
 
     public Builder setServerApproveAutorenewEvent(
         VKey<BillingEvent.Recurring> serverApproveAutorenewEvent) {
       getInstance().serverApproveAutorenewEvent = serverApproveAutorenewEvent;
-      getInstance().serverApproveAutorenewEventHistoryId =
-          DomainBase.getHistoryId(serverApproveAutorenewEvent);
       return this;
     }
 
     public Builder setServerApproveAutorenewPollMessage(
         VKey<PollMessage.Autorenew> serverApproveAutorenewPollMessage) {
       getInstance().serverApproveAutorenewPollMessage = serverApproveAutorenewPollMessage;
-      getInstance().serverApproveAutorenewPollMessageHistoryId =
+      return this;
-          DomainBase.getHistoryId(serverApproveAutorenewPollMessage);
+    }
+
+    @Override
+    public Builder setServerApproveEntities(
+        String repoId,
+        Long historyId,
+        ImmutableSet<VKey<? extends TransferServerApproveEntity>> serverApproveEntities) {
+      super.setServerApproveEntities(repoId, historyId, serverApproveEntities);
+      mapBillingCancellationEntityToField(serverApproveEntities, getInstance());
       return this;
     }
   }

core/src/main/java/google/registry/model/transfer/TransferData.java

@@ -14,26 +14,20 @@
 
 package google.registry.model.transfer;
 
+import static com.google.common.base.Preconditions.checkState;
 import static com.google.common.collect.ImmutableList.toImmutableList;
 import static google.registry.util.CollectionUtils.isNullOrEmpty;
 import static google.registry.util.CollectionUtils.nullToEmpty;
-import static google.registry.util.CollectionUtils.nullToEmptyImmutableCopy;
 
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
-import com.googlecode.objectify.Key;
-import com.googlecode.objectify.annotation.AlsoLoad;
 import com.googlecode.objectify.annotation.Ignore;
-import com.googlecode.objectify.annotation.IgnoreSave;
-import com.googlecode.objectify.condition.IfNull;
 import google.registry.model.Buildable;
 import google.registry.model.EppResource;
-import google.registry.model.contact.ContactResource;
-import google.registry.model.domain.DomainBase;
 import google.registry.model.eppcommon.Trid;
 import google.registry.model.poll.PollMessage;
-import google.registry.model.reporting.HistoryEntry;
 import google.registry.persistence.VKey;
+import google.registry.util.NullIgnoringCollectionBuilder;
 import google.registry.util.TypeUtils.TypeInstantiator;
 import java.util.Set;
 import javax.annotation.Nullable;
@@ -42,8 +36,6 @@ import javax.persistence.AttributeOverrides;
 import javax.persistence.Column;
 import javax.persistence.Embedded;
 import javax.persistence.MappedSuperclass;
-import javax.persistence.PostLoad;
-import javax.persistence.Transient;
 
 /**
  * Common transfer data for {@link EppResource} types. Only applies to domains and contacts; hosts
@@ -66,20 +58,6 @@ public abstract class TransferData<
   })
   Trid transferRequestTrid;
 
-  /**
-   * The billing event and poll messages associated with a server-approved transfer.
-   *
-   * <p>This field should be null if there is not currently a pending transfer or if the object
-   * being transferred is not a domain. If there is a pending transfer for a domain there should be
-   * a number of poll messages and billing events for both the gaining and losing registrars. If the
-   * pending transfer is explicitly approved, rejected or cancelled, the referenced entities should
-   * be deleted.
-   */
-  @Transient
-  @DoNotCompare
-  @IgnoreSave(IfNull.class)
-  Set<VKey<? extends TransferServerApproveEntity>> serverApproveEntities;
-
   @Ignore
   @Column(name = "transfer_repo_id")
   String repoId;
@@ -89,11 +67,7 @@ public abstract class TransferData<
   Long historyEntryId;
 
   // The pollMessageId1 and pollMessageId2 are used to store the IDs for gaining and losing poll
-  // messages in Cloud SQL, and they are added to replace the VKeys in serverApproveEntities.
+  // messages in Cloud SQL.
-  // Although we can distinguish which is which when we construct the TransferData instance from
-  // the transfer request flow, when the instance is loaded from Datastore, we cannot make this
-  // distinction because they are just VKeys. Also, the only way we use serverApproveEntities is to
-  // just delete all the entities referenced by the VKeys, so we don't need to make the distinction.
   //
   // In addition, there may be a third poll message for the autorenew poll message on domain
   // transfer if applicable.
@@ -111,13 +85,23 @@ public abstract class TransferData<
 
   public abstract boolean isEmpty();
 
+  public Long getHistoryEntryId() {
+    return historyEntryId;
+  }
+
   @Nullable
   public Trid getTransferRequestTrid() {
     return transferRequestTrid;
   }
 
   public ImmutableSet<VKey<? extends TransferServerApproveEntity>> getServerApproveEntities() {
-    return nullToEmptyImmutableCopy(serverApproveEntities);
+    return NullIgnoringCollectionBuilder.create(
+            new ImmutableSet.Builder<VKey<? extends TransferServerApproveEntity>>())
+        .add(pollMessageId1 != null ? VKey.createSql(PollMessage.class, pollMessageId1) : null)
+        .add(pollMessageId2 != null ? VKey.createSql(PollMessage.class, pollMessageId2) : null)
+        .add(pollMessageId3 != null ? VKey.createSql(PollMessage.class, pollMessageId3) : null)
+        .getBuilder()
+        .build();
   }
 
   @Override
@@ -147,67 +131,16 @@ public abstract class TransferData<
     return newBuilder;
   }
 
-  void onLoad(
-      @AlsoLoad("serverApproveEntities")
-          Set<VKey<? extends TransferServerApproveEntity>> serverApproveEntities) {
-    mapServerApproveEntitiesToFields(serverApproveEntities, this);
-  }
-
-  @PostLoad
-  void postLoad() {
-    mapFieldsToServerApproveEntities();
-  }
-
-  /**
-   * Reconstructs serverApproveEntities set from the individual fields, e.g. repoId, historyEntryId,
-   * pollMessageId1.
-   */
-  void mapFieldsToServerApproveEntities() {
-    if (repoId == null) {
-      return;
-    }
-    Key<? extends EppResource> eppKey;
-    if (getClass().equals(DomainTransferData.class)) {
-      eppKey = Key.create(DomainBase.class, repoId);
-    } else {
-      eppKey = Key.create(ContactResource.class, repoId);
-    }
-    Key<HistoryEntry> historyEntryKey = Key.create(eppKey, HistoryEntry.class, historyEntryId);
-    ImmutableSet.Builder<VKey<? extends TransferServerApproveEntity>> entityKeysBuilder =
-        new ImmutableSet.Builder<>();
-    if (pollMessageId1 != null) {
-      Key<PollMessage> ofyKey = Key.create(historyEntryKey, PollMessage.class, pollMessageId1);
-      entityKeysBuilder.add(PollMessage.createVKey(ofyKey));
-    }
-    if (pollMessageId2 != null) {
-      Key<PollMessage> ofyKey = Key.create(historyEntryKey, PollMessage.class, pollMessageId2);
-      entityKeysBuilder.add(PollMessage.createVKey(ofyKey));
-    }
-    if (pollMessageId3 != null) {
-      Key<PollMessage> ofyKey = Key.create(historyEntryKey, PollMessage.class, pollMessageId3);
-      entityKeysBuilder.add(PollMessage.createVKey(ofyKey));
-    }
-    serverApproveEntities = entityKeysBuilder.build();
-  }
-
   /** Maps serverApproveEntities set to the individual fields. */
   static void mapServerApproveEntitiesToFields(
       Set<VKey<? extends TransferServerApproveEntity>> serverApproveEntities,
       TransferData transferData) {
     if (isNullOrEmpty(serverApproveEntities)) {
-      transferData.historyEntryId = null;
-      transferData.repoId = null;
       transferData.pollMessageId1 = null;
       transferData.pollMessageId2 = null;
       transferData.pollMessageId3 = null;
       return;
     }
-    // Each element in serverApproveEntities should have the exact same Key<HistoryEntry> as its
-    // parent. So, we can use any to set historyEntryId and repoId.
-    Key<?> key = serverApproveEntities.iterator().next().getOfyKey();
-    transferData.historyEntryId = key.getParent().getId();
-    transferData.repoId = key.getParent().getParent().getName();
-
     ImmutableList<Long> sortedPollMessageIds = getSortedPollMessageIds(serverApproveEntities);
     if (sortedPollMessageIds.size() >= 1) {
       transferData.pollMessageId1 = sortedPollMessageIds.get(0);
@@ -250,14 +183,21 @@ public abstract class TransferData<
     }
 
     public B setServerApproveEntities(
+        String repoId,
+        Long historyId,
         ImmutableSet<VKey<? extends TransferServerApproveEntity>> serverApproveEntities) {
-      getInstance().serverApproveEntities = serverApproveEntities;
+      getInstance().repoId = repoId;
+      getInstance().historyEntryId = historyId;
+      mapServerApproveEntitiesToFields(serverApproveEntities, getInstance());
       return thisCastToDerived();
     }
 
     @Override
     public T build() {
-      mapServerApproveEntitiesToFields(getInstance().serverApproveEntities, getInstance());
+      if (getInstance().pollMessageId1 != null) {
+        checkState(getInstance().repoId != null, "Repo id undefined");
+        checkState(getInstance().historyEntryId != null, "History entry undefined");
+      }
       return super.build();
     }
   }

core/src/main/java/google/registry/model/translators/EppHistoryVKeyTranslatorFactory.java

@@ -103,7 +103,7 @@ public class EppHistoryVKeyTranslatorFactory
       @Nullable
       @Override
       public Key saveValue(@Nullable EppHistoryVKey pojoValue) {
-        return pojoValue == null ? null : pojoValue.createOfyKey().getRaw();
+        throw new UnsupportedOperationException("saveValue for EppHistory keys removed.");
       }
     };
   }

core/src/main/java/google/registry/persistence/BillingVKey.java

@@ -69,11 +69,6 @@ public abstract class BillingVKey<K> extends EppHistoryVKey<K, DomainBase> {
       super(repoId, historyRevisionId, billingEventId);
     }
 
-    @Override
-    public Key<OneTime> createOfyKey() {
-      return Key.create(createHistoryEntryKey(), BillingEvent.OneTime.class, billingId);
-    }
-
     /** Creates a {@link BillingEventVKey} instance from the given {@link Key} instance. */
     public static BillingEventVKey create(@Nullable Key<BillingEvent.OneTime> ofyKey) {
       if (ofyKey == null) {
@@ -87,7 +82,7 @@ public abstract class BillingVKey<K> extends EppHistoryVKey<K, DomainBase> {
 
     /** Creates a {@link BillingEventVKey} instance from the given {@link VKey} instance. */
     public static BillingEventVKey create(@Nullable VKey<BillingEvent.OneTime> vKey) {
-      return vKey == null ? null : create(vKey.getOfyKey());
+      return vKey == null ? null : new BillingEventVKey(null, 0, (Long) vKey.getSqlKey());
     }
   }
 
@@ -111,11 +106,6 @@ public abstract class BillingVKey<K> extends EppHistoryVKey<K, DomainBase> {
       super(repoId, historyRevisionId, billingEventId);
     }
 
-    @Override
-    public Key<Recurring> createOfyKey() {
-      return Key.create(createHistoryEntryKey(), BillingEvent.Recurring.class, billingId);
-    }
-
     /** Creates a {@link BillingRecurrenceVKey} instance from the given {@link Key} instance. */
     public static BillingRecurrenceVKey create(@Nullable Key<BillingEvent.Recurring> ofyKey) {
       if (ofyKey == null) {
@@ -129,7 +119,7 @@ public abstract class BillingVKey<K> extends EppHistoryVKey<K, DomainBase> {
 
     /** Creates a {@link BillingRecurrenceVKey} instance from the given {@link VKey} instance. */
     public static BillingRecurrenceVKey create(@Nullable VKey<BillingEvent.Recurring> vKey) {
-      return vKey == null ? null : create(vKey.getOfyKey());
+      return vKey == null ? null : new BillingRecurrenceVKey(null, 0, (Long) vKey.getSqlKey());
     }
   }
 }

core/src/main/java/google/registry/persistence/DomainHistoryVKey.java

@@ -40,11 +40,6 @@ public class DomainHistoryVKey extends EppHistoryVKey<HistoryEntry, DomainBase>
     return new DomainHistoryId(repoId, historyRevisionId);
   }
 
-  @Override
-  public Key<HistoryEntry> createOfyKey() {
-    return Key.create(Key.create(DomainBase.class, repoId), HistoryEntry.class, historyRevisionId);
-  }
-
   /** Creates {@link DomainHistoryVKey} from the given {@link Key} instance. */
   public static DomainHistoryVKey create(Key<? extends HistoryEntry> ofyKey) {
     checkArgumentNotNull(ofyKey, "ofyKey must be specified");

core/src/main/java/google/registry/persistence/EppHistoryVKey.java

@@ -99,10 +99,8 @@ public abstract class EppHistoryVKey<K, E extends EppResource> extends Immutable
   @Override
   public VKey<K> createVKey() {
     Class<K> vKeyType = new TypeInstantiator<K>(getClass()) {}.getExactType();
-    return VKey.create(vKeyType, createSqlKey(), createOfyKey());
+    return VKey.createSql(vKeyType, createSqlKey());
   }
 
   public abstract Serializable createSqlKey();
-
-  public abstract Key<K> createOfyKey();
 }

core/src/main/java/google/registry/persistence/VKey.java

@@ -16,6 +16,7 @@ package google.registry.persistence;
 
 import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkState;
+import static google.registry.model.ImmutableObject.Insignificant;
 import static google.registry.util.PreconditionsUtils.checkArgumentNotNull;
 
 import com.google.common.base.Splitter;
@@ -52,7 +53,8 @@ public class VKey<T> extends ImmutableObject implements Serializable {
   // The SQL key for the referenced entity.
   Serializable sqlKey;
 
-  // The objectify key for the referenced entity.
+  // The objectify key for the referenced entity.  Marked Insignificant to exclude it from
+  // hashing/equality.
   @Insignificant Key<T> ofyKey;
 
   Class<? extends T> kind;

core/src/main/java/google/registry/tools/EnqueuePollMessageCommand.java

@@ -118,7 +118,7 @@ class EnqueuePollMessageCommand extends MutatingCommand {
                     null,
                     new PollMessage.OneTime.Builder()
                         .setRegistrarId(registrarId)
-                        .setParent(historyEntry)
+                        .setHistoryEntry(historyEntry)
                         .setEventTime(tm().getTransactionTime())
                         .setMsg(message)
                         .build());

core/src/main/java/google/registry/tools/UnrenewDomainCommand.java

@@ -201,7 +201,7 @@ class UnrenewDomainCommand extends ConfirmingCommand implements CommandWithRemot
                 String.format(
                     "Domain %s was unrenewed by %d years; now expires at %s.",
                     domainName, period, newExpirationTime))
-            .setParent(domainHistory)
+            .setHistoryEntry(domainHistory)
             .setEventTime(now)
             .build();
     // Create a new autorenew billing event and poll message starting at the new expiration time.
@@ -213,7 +213,7 @@ class UnrenewDomainCommand extends ConfirmingCommand implements CommandWithRemot
     PollMessage.Autorenew newAutorenewPollMessage =
         newAutorenewPollMessage(domain)
             .setEventTime(newExpirationTime)
-            .setParent(domainHistory)
+            .setHistoryEntry(domainHistory)
             .build();
     // End the old autorenew billing event and poll message now.
     updateAutorenewRecurrenceEndTime(domain, now);
@@ -224,7 +224,9 @@ class UnrenewDomainCommand extends ConfirmingCommand implements CommandWithRemot
             .setLastEppUpdateTime(now)
             .setLastEppUpdateRegistrarId(domain.getCurrentSponsorRegistrarId())
             .setAutorenewBillingEvent(newAutorenewEvent.createVKey())
-            .setAutorenewPollMessage(newAutorenewPollMessage.createVKey())
+            .setAutorenewPollMessage(
+                newAutorenewPollMessage.createVKey(),
+                newAutorenewPollMessage.getHistoryRevisionId())
             .build();
     // In order to do it'll need to write out a new HistoryEntry (likely of type SYNTHETIC), a new
     // autorenew billing event and poll message, and a new one time poll message at the present time

core/src/test/java/google/registry/batch/DeleteExpiredDomainsActionTest.java

@@ -191,7 +191,8 @@ class DeleteExpiredDomainsActionTest {
                 .asBuilder()
                 .setAutorenewEndTime(Optional.of(clock.nowUtc().minusDays(10)))
                 .setAutorenewBillingEvent(autorenewBillingEvent.createVKey())
-                .setAutorenewPollMessage(autorenewPollMessage.createVKey())
+                .setAutorenewPollMessage(
+                    autorenewPollMessage.createVKey(), autorenewPollMessage.getHistoryRevisionId())
                 .build());
 
     return pendingExpirationDomain;
@@ -216,6 +217,6 @@ class DeleteExpiredDomainsActionTest {
         .setRegistrarId("TheRegistrar")
         .setEventTime(clock.nowUtc().plusYears(1))
         .setAutorenewEndTime(END_OF_TIME)
-        .setParent(createHistoryEntry);
+        .setHistoryEntry(createHistoryEntry);
   }
 }

core/src/test/java/google/registry/batch/DeleteProberDataActionTest.java

@@ -316,7 +316,7 @@ class DeleteProberDataActionTest {
     PollMessage.OneTime pollMessage =
         persistSimpleResource(
             new PollMessage.OneTime.Builder()
-                .setParent(historyEntry)
+                .setHistoryEntry(historyEntry)
                 .setEventTime(DELETION_TIME)
                 .setRegistrarId("TheRegistrar")
                 .setMsg("Domain registered")

core/src/test/java/google/registry/beam/rde/RdePipelineTest.java

@@ -311,6 +311,10 @@ public class RdePipelineTest {
     persistDomainHistory(
         helloDomain
             .asBuilder()
+            .removeContacts(
+                helloDomain.getContacts().stream()
+                    .filter(dc -> dc.getType() == DesignatedContact.Type.ADMIN)
+                    .collect(toImmutableSet()))
             .addContacts(
                 ImmutableSet.of(
                     DesignatedContact.create(DesignatedContact.Type.ADMIN, contact3.createVKey())))

core/src/test/java/google/registry/flows/contact/ContactTransferRequestFlowTest.java

@@ -107,6 +107,8 @@ class ContactTransferRequestFlowTest
                 // Make the server-approve entities field a no-op comparison; it's easier to
                 // do this comparison separately below.
                 .setServerApproveEntities(
+                    contact.getRepoId(),
+                    contact.getTransferData().getHistoryEntryId(),
                     forceEmptyToNull(contact.getTransferData().getServerApproveEntities()))
                 .build());
     assertNoBillingEvents();

core/src/test/java/google/registry/flows/custom/TestDomainCreateFlowCustomLogic.java

@@ -34,7 +34,7 @@ public class TestDomainCreateFlowCustomLogic extends DomainCreateFlowCustomLogic
     if (parameters.newDomain().getDomainName().startsWith("custom-logic-test")) {
       PollMessage extraPollMessage =
           new PollMessage.OneTime.Builder()
-              .setParent(parameters.historyEntry())
+              .setHistoryEntry(parameters.historyEntry())
               .setEventTime(tm().getTransactionTime())
               .setRegistrarId(getSessionMetadata().get().getRegistrarId())
               .setMsg("Custom logic was triggered")

core/src/test/java/google/registry/flows/domain/DomainCreateFlowTest.java

@@ -348,7 +348,7 @@ class DomainCreateFlowTest extends ResourceFlowTestCase<DomainCreateFlow, Domain
             .setRegistrarId("TheRegistrar")
             .setEventTime(domain.getRegistrationExpirationTime())
             .setMsg("Domain was auto-renewed.")
-            .setParent(historyEntry)
+            .setHistoryEntry(historyEntry)
             .build());
 
     assertGracePeriods(
@@ -1656,10 +1656,10 @@ class DomainCreateFlowTest extends ResourceFlowTestCase<DomainCreateFlow, Domain
             .setRegistrarId("TheRegistrar")
             .setEventTime(domain.getRegistrationExpirationTime())
             .setMsg("Domain was auto-renewed.")
-            .setParent(historyEntry)
+            .setHistoryEntry(historyEntry)
             .build(),
         new PollMessage.OneTime.Builder()
-            .setParent(historyEntry)
+            .setHistoryEntry(historyEntry)
             .setEventTime(domain.getCreationTime())
             .setRegistrarId("TheRegistrar")
             .setMsg(DomainFlowUtils.COLLISION_MESSAGE)
@@ -1811,10 +1811,10 @@ class DomainCreateFlowTest extends ResourceFlowTestCase<DomainCreateFlow, Domain
             .setRegistrarId("TheRegistrar")
             .setEventTime(domain.getRegistrationExpirationTime())
             .setMsg("Domain was auto-renewed.")
-            .setParent(historyEntry)
+            .setHistoryEntry(historyEntry)
             .build(),
         new PollMessage.OneTime.Builder()
-            .setParent(historyEntry)
+            .setHistoryEntry(historyEntry)
             .setEventTime(domain.getCreationTime())
             .setRegistrarId("TheRegistrar")
             .setMsg("Custom logic was triggered")

core/src/test/java/google/registry/flows/domain/DomainDeleteFlowTest.java

@@ -149,7 +149,8 @@ class DomainDeleteFlowTest extends ResourceFlowTestCase<DomainDeleteFlow, Domain
             domain
                 .asBuilder()
                 .setAutorenewBillingEvent(autorenewBillingEvent.createVKey())
-                .setAutorenewPollMessage(autorenewPollMessage.createVKey())
+                .setAutorenewPollMessage(
+                    autorenewPollMessage.createVKey(), autorenewPollMessage.getHistoryRevisionId())
                 .build());
 
     assertTransactionalFlow(true);
@@ -215,7 +216,8 @@ class DomainDeleteFlowTest extends ResourceFlowTestCase<DomainDeleteFlow, Domain
                             "TheRegistrar",
                             autorenewBillingEvent.createVKey())))
                 .setAutorenewBillingEvent(autorenewBillingEvent.createVKey())
-                .setAutorenewPollMessage(autorenewPollMessage.createVKey())
+                .setAutorenewPollMessage(
+                    autorenewPollMessage.createVKey(), autorenewPollMessage.getHistoryRevisionId())
                 .build());
     assertTransactionalFlow(true);
   }
@@ -281,7 +283,7 @@ class DomainDeleteFlowTest extends ResourceFlowTestCase<DomainDeleteFlow, Domain
         .setRegistrarId(registrarId)
         .setEventTime(A_MONTH_FROM_NOW)
         .setAutorenewEndTime(END_OF_TIME)
-        .setParent(earlierHistoryEntry);
+        .setHistoryEntry(earlierHistoryEntry);
   }
 
   @TestOfyAndSql
@@ -481,8 +483,8 @@ class DomainDeleteFlowTest extends ResourceFlowTestCase<DomainDeleteFlow, Domain
     DateTime deletionTime = domain.getDeletionTime();
     assertThat(getPollMessages("TheRegistrar", deletionTime.minusMinutes(1))).isEmpty();
     assertThat(getPollMessages("TheRegistrar", deletionTime)).hasSize(1);
-    assertThat(domain.getDeletePollMessage().getOfyKey())
+    assertThat(domain.getDeletePollMessage())
-        .isEqualTo(getOnlyPollMessage("TheRegistrar").createVKey().getOfyKey());
+        .isEqualTo(getOnlyPollMessage("TheRegistrar").createVKey());
     PollMessage.OneTime deletePollMessage = loadByKey(domain.getDeletePollMessage());
     assertThat(deletePollMessage.getMsg()).isEqualTo(expectedMessage);
   }
@@ -841,7 +843,7 @@ class DomainDeleteFlowTest extends ResourceFlowTestCase<DomainDeleteFlow, Domain
     assertPollMessages(
         new PollMessage.OneTime.Builder()
             .setRegistrarId("TheRegistrar")
-            .setParent(deleteHistoryEntry)
+            .setHistoryEntry(deleteHistoryEntry)
             .setEventTime(now)
             .setMsg(
                 "Domain example.tld was deleted by registry administrator with final deletion"
@@ -853,7 +855,7 @@ class DomainDeleteFlowTest extends ResourceFlowTestCase<DomainDeleteFlow, Domain
             .build(),
         new PollMessage.OneTime.Builder()
             .setRegistrarId("TheRegistrar")
-            .setParent(deleteHistoryEntry)
+            .setHistoryEntry(deleteHistoryEntry)
             .setEventTime(DateTime.parse("2000-07-11T22:00:00.012Z"))
             .setMsg("Deleted by registry administrator.")
             .setResponseData(

core/src/test/java/google/registry/flows/domain/DomainRenewFlowTest.java

@@ -169,7 +169,7 @@ class DomainRenewFlowTest extends ResourceFlowTestCase<DomainRenewFlow, DomainBa
                         .setEventTime(expirationTime)
                         .setAutorenewEndTime(END_OF_TIME)
                         .setMsg("Domain was auto-renewed.")
-                        .setParent(historyEntryDomainCreate)
+                        .setHistoryEntry(historyEntryDomainCreate)
                         .build();
                 DomainBase newDomain =
                     domain
@@ -177,7 +177,9 @@ class DomainRenewFlowTest extends ResourceFlowTestCase<DomainRenewFlow, DomainBa
                         .setRegistrationExpirationTime(expirationTime)
                         .setStatusValues(ImmutableSet.copyOf(statusValues))
                         .setAutorenewBillingEvent(autorenewEvent.createVKey())
-                        .setAutorenewPollMessage(autorenewPollMessage.createVKey())
+                        .setAutorenewPollMessage(
+                            autorenewPollMessage.createVKey(),
+                            autorenewPollMessage.getHistoryRevisionId())
                         .build();
                 persistResources(
                     ImmutableSet.of(
@@ -307,7 +309,7 @@ class DomainRenewFlowTest extends ResourceFlowTestCase<DomainRenewFlow, DomainBa
             .setEventTime(domain.getRegistrationExpirationTime())
             .setAutorenewEndTime(END_OF_TIME)
             .setMsg("Domain was auto-renewed.")
-            .setParent(historyEntryDomainRenew)
+            .setHistoryEntry(historyEntryDomainRenew)
             .build());
     assertGracePeriods(
         domain.getGracePeriods(),
@@ -647,7 +649,7 @@ class DomainRenewFlowTest extends ResourceFlowTestCase<DomainRenewFlow, DomainBa
             .setEventTime(expirationTime.minusYears(1))
             .setAutorenewEndTime(clock.nowUtc())
             .setMsg("Domain was auto-renewed.")
-            .setParent(
+            .setHistoryEntry(
                 getOnlyHistoryEntryOfType(
                     reloadResourceByForeignKey(), HistoryEntry.Type.DOMAIN_CREATE))
             .build(),
@@ -657,7 +659,7 @@ class DomainRenewFlowTest extends ResourceFlowTestCase<DomainRenewFlow, DomainBa
             .setEventTime(reloadResourceByForeignKey().getRegistrationExpirationTime())
             .setAutorenewEndTime(END_OF_TIME)
             .setMsg("Domain was auto-renewed.")
-            .setParent(historyEntryDomainRenew)
+            .setHistoryEntry(historyEntryDomainRenew)
             .build());
   }
 

core/src/test/java/google/registry/flows/domain/DomainRestoreRequestFlowTest.java

@@ -139,7 +139,7 @@ class DomainRestoreRequestFlowTest
                         new PollMessage.OneTime.Builder()
                             .setRegistrarId("TheRegistrar")
                             .setEventTime(clock.nowUtc().plusDays(5))
-                            .setParent(historyEntry)
+                            .setHistoryEntry(historyEntry)
                             .build())
                     .createVKey())
             .build());
@@ -202,7 +202,7 @@ class DomainRestoreRequestFlowTest
             .setEventTime(domain.getRegistrationExpirationTime())
             .setAutorenewEndTime(END_OF_TIME)
             .setMsg("Domain was auto-renewed.")
-            .setParent(historyEntryDomainRestore)
+            .setHistoryEntry(historyEntryDomainRestore)
             .build());
     // There should be a onetime for the restore and a new recurring billing event, but no renew
     // onetime.
@@ -271,7 +271,7 @@ class DomainRestoreRequestFlowTest
             .setEventTime(domain.getRegistrationExpirationTime())
             .setAutorenewEndTime(END_OF_TIME)
             .setMsg("Domain was auto-renewed.")
-            .setParent(historyEntryDomainRestore)
+            .setHistoryEntry(historyEntryDomainRestore)
             .build());
     // There should be a bill for the restore and an explicit renew, along with a new recurring
     // autorenew event.

core/src/test/java/google/registry/flows/domain/DomainTransferCancelFlowTest.java

@@ -97,7 +97,7 @@ class DomainTransferCancelFlowTest
             .setEventTime(EXTENDED_REGISTRATION_EXPIRATION_TIME)
             .setAutorenewEndTime(END_OF_TIME)
             .setMsg("Domain was auto-renewed.")
-            .setParent(historyEntryDomainTransferRequest)
+            .setHistoryEntry(historyEntryDomainTransferRequest)
             .build(),
         createPollMessageForImplicitTransfer(
             domain,
@@ -164,7 +164,7 @@ class DomainTransferCancelFlowTest
             .setEventTime(originalExpirationTime)
             .setAutorenewEndTime(END_OF_TIME)
             .setMsg("Domain was auto-renewed.")
-            .setParent(getOnlyHistoryEntryOfType(domain, DOMAIN_CREATE))
+            .setHistoryEntry(getOnlyHistoryEntryOfType(domain, DOMAIN_CREATE))
             .build(),
         new PollMessage.OneTime.Builder()
             .setRegistrarId("TheRegistrar")
@@ -180,7 +180,7 @@ class DomainTransferCancelFlowTest
                         .setPendingTransferExpirationTime(clock.nowUtc())
                         .build()))
             .setMsg("Transfer cancelled.")
-            .setParent(getOnlyHistoryEntryOfType(domain, DOMAIN_TRANSFER_CANCEL))
+            .setHistoryEntry(getOnlyHistoryEntryOfType(domain, DOMAIN_TRANSFER_CANCEL))
             .build());
 
     // The original grace periods should remain untouched.

core/src/test/java/google/registry/flows/domain/DomainUpdateFlowTest.java

@@ -1160,7 +1160,7 @@ class DomainUpdateFlowTest extends ResourceFlowTestCase<DomainUpdateFlow, Domain
         updatedDomain,
         new PollMessage.OneTime.Builder()
             .setEventTime(clock.nowUtc())
-            .setParent(getOnlyHistoryEntryOfType(updatedDomain, DOMAIN_UPDATE))
+            .setHistoryEntry(getOnlyHistoryEntryOfType(updatedDomain, DOMAIN_UPDATE))
             .setRegistrarId("NewRegistrar")
             .setMsg("The registry administrator has added the status(es) [serverHold].")
             .setResponseData(
@@ -1199,7 +1199,7 @@ class DomainUpdateFlowTest extends ResourceFlowTestCase<DomainUpdateFlow, Domain
         updatedDomain,
         new PollMessage.OneTime.Builder()
             .setEventTime(clock.nowUtc())
-            .setParent(getOnlyHistoryEntryOfType(updatedDomain, DOMAIN_UPDATE))
+            .setHistoryEntry(getOnlyHistoryEntryOfType(updatedDomain, DOMAIN_UPDATE))
             .setRegistrarId("NewRegistrar")
             .setMsg(
                 "The registry administrator has removed the status(es) [serverHold,"
@@ -1237,7 +1237,7 @@ class DomainUpdateFlowTest extends ResourceFlowTestCase<DomainUpdateFlow, Domain
         updatedDomain,
         new PollMessage.OneTime.Builder()
             .setEventTime(clock.nowUtc())
-            .setParent(getOnlyHistoryEntryOfType(updatedDomain, DOMAIN_UPDATE))
+            .setHistoryEntry(getOnlyHistoryEntryOfType(updatedDomain, DOMAIN_UPDATE))
             .setRegistrarId("NewRegistrar")
             .setMsg(
                 "The registry administrator has added the status(es) [serverHold,"

core/src/test/java/google/registry/flows/poll/PollAckFlowTest.java

@@ -70,7 +70,7 @@ class PollAckFlowTest extends FlowTestCase<PollAckFlow> {
             .setRegistrarId(getRegistrarIdForFlow())
             .setEventTime(clock.nowUtc().minusDays(1))
             .setMsg("Some poll message.")
-            .setParent(createHistoryEntryForEppResource(domain))
+            .setHistoryEntry(createHistoryEntryForEppResource(domain))
             .build());
   }
 
@@ -83,7 +83,7 @@ class PollAckFlowTest extends FlowTestCase<PollAckFlow> {
             .setAutorenewEndTime(endTime)
             .setMsg("Domain was auto-renewed.")
             .setTargetId("example.com")
-            .setParent(createHistoryEntryForEppResource(domain))
+            .setHistoryEntry(createHistoryEntryForEppResource(domain))
             .build());
   }
 
@@ -102,7 +102,7 @@ class PollAckFlowTest extends FlowTestCase<PollAckFlow> {
             .setRegistrarId(getRegistrarIdForFlow())
             .setEventTime(clock.nowUtc().minusDays(1))
             .setMsg("Some poll message.")
-            .setParent(createHistoryEntryForEppResource(contact))
+            .setHistoryEntry(createHistoryEntryForEppResource(contact))
             .build());
     assertTransactionalFlow(true);
     runFlowAssertResponse(loadFile("poll_ack_response_empty.xml"));
@@ -117,7 +117,7 @@ class PollAckFlowTest extends FlowTestCase<PollAckFlow> {
             .setRegistrarId(getRegistrarIdForFlow())
             .setEventTime(clock.nowUtc().minusDays(1))
             .setMsg("Some poll message.")
-            .setParent(createHistoryEntryForEppResource(contact))
+            .setHistoryEntry(createHistoryEntryForEppResource(contact))
             .build());
     assertTransactionalFlow(true);
     assertThrows(MessageDoesNotExistException.class, this::runFlow);
@@ -205,7 +205,7 @@ class PollAckFlowTest extends FlowTestCase<PollAckFlow> {
             .setRegistrarId(getRegistrarIdForFlow())
             .setEventTime(clock.nowUtc().minusDays(1))
             .setMsg("Some poll message.")
-            .setParent(createHistoryEntryForEppResource(contact))
+            .setHistoryEntry(createHistoryEntryForEppResource(contact))
             .build());
     assertTransactionalFlow(true);
     assertThrows(InvalidMessageIdException.class, this::runFlow);
@@ -240,7 +240,7 @@ class PollAckFlowTest extends FlowTestCase<PollAckFlow> {
             .setRegistrarId("TheRegistrar")
             .setEventTime(clock.nowUtc().minusDays(1))
             .setMsg("Some poll message.")
-            .setParent(createHistoryEntryForEppResource(domain))
+            .setHistoryEntry(createHistoryEntryForEppResource(domain))
             .build());
     assertTransactionalFlow(true);
     assertThrows(NotAuthorizedToAckMessageException.class, this::runFlow);
@@ -254,7 +254,7 @@ class PollAckFlowTest extends FlowTestCase<PollAckFlow> {
             .setRegistrarId(getRegistrarIdForFlow())
             .setEventTime(clock.nowUtc().plusDays(1))
             .setMsg("Some poll message.")
-            .setParent(createHistoryEntryForEppResource(domain))
+            .setHistoryEntry(createHistoryEntryForEppResource(domain))
             .build());
     assertTransactionalFlow(true);
     Exception e = assertThrows(MessageDoesNotExistException.class, this::runFlow);

core/src/test/java/google/registry/flows/poll/PollRequestFlowTest.java

@@ -87,7 +87,7 @@ class PollRequestFlowTest extends FlowTestCase<PollRequestFlow> {
                         .setPendingTransferExpirationTime(clock.nowUtc().minusDays(1))
                         .setExtendedRegistrationExpirationTime(clock.nowUtc().plusYears(1))
                         .build()))
-            .setParent(createHistoryEntryForEppResource(domain))
+            .setHistoryEntry(createHistoryEntryForEppResource(domain))
             .build());
   }
 
@@ -125,7 +125,7 @@ class PollRequestFlowTest extends FlowTestCase<PollRequestFlow> {
                         .setLosingRegistrarId("NewRegistrar")
                         .setPendingTransferExpirationTime(clock.nowUtc())
                         .build()))
-            .setParent(createHistoryEntryForEppResource(contact))
+            .setHistoryEntry(createHistoryEntryForEppResource(contact))
             .build());
     assertTransactionalFlow(false);
     runFlowAssertResponse(loadFile("poll_response_contact_transfer.xml"));
@@ -145,7 +145,7 @@ class PollRequestFlowTest extends FlowTestCase<PollRequestFlow> {
                         true,
                         Trid.create("ABC-12345", "other-trid"),
                         clock.nowUtc())))
-            .setParent(createHistoryEntryForEppResource(domain))
+            .setHistoryEntry(createHistoryEntryForEppResource(domain))
             .build());
     assertTransactionalFlow(false);
     runFlowAssertResponse(loadFile("poll_response_domain_pending_notification.xml"));
@@ -169,7 +169,7 @@ class PollRequestFlowTest extends FlowTestCase<PollRequestFlow> {
                         true,
                         Trid.create("ABC-12345", "other-trid"),
                         clock.nowUtc())))
-            .setParent(createHistoryEntryForEppResource(domain))
+            .setHistoryEntry(createHistoryEntryForEppResource(domain))
             .build());
     assertTransactionalFlow(false);
     runFlowAssertResponse(loadFile("poll_message_domain_pending_action_immediate_delete.xml"));
@@ -183,7 +183,7 @@ class PollRequestFlowTest extends FlowTestCase<PollRequestFlow> {
             .setEventTime(clock.nowUtc().minusDays(1))
             .setMsg("Domain was auto-renewed.")
             .setTargetId("test.example")
-            .setParent(createHistoryEntryForEppResource(domain))
+            .setHistoryEntry(createHistoryEntryForEppResource(domain))
             .build());
     assertTransactionalFlow(false);
     runFlowAssertResponse(loadFile("poll_response_autorenew.xml"));
@@ -201,7 +201,7 @@ class PollRequestFlowTest extends FlowTestCase<PollRequestFlow> {
             .setRegistrarId("BadRegistrar")
             .setEventTime(clock.nowUtc().minusDays(1))
             .setMsg("Poll message")
-            .setParent(createHistoryEntryForEppResource(domain))
+            .setHistoryEntry(createHistoryEntryForEppResource(domain))
             .build());
     runFlowAssertResponse(loadFile("poll_response_empty.xml"));
   }
@@ -213,7 +213,7 @@ class PollRequestFlowTest extends FlowTestCase<PollRequestFlow> {
             .setRegistrarId(getRegistrarIdForFlow())
             .setEventTime(clock.nowUtc().plusDays(1))
             .setMsg("Poll message")
-            .setParent(createHistoryEntryForEppResource(domain))
+            .setHistoryEntry(createHistoryEntryForEppResource(domain))
             .build());
     runFlowAssertResponse(loadFile("poll_response_empty.xml"));
   }
@@ -226,7 +226,7 @@ class PollRequestFlowTest extends FlowTestCase<PollRequestFlow> {
             .setEventTime(clock.nowUtc().plusDays(1))
             .setMsg("Domain was auto-renewed.")
             .setTargetId("target.example")
-            .setParent(createHistoryEntryForEppResource(domain))
+            .setHistoryEntry(createHistoryEntryForEppResource(domain))
             .build());
     assertTransactionalFlow(false);
     runFlowAssertResponse(loadFile("poll_response_empty.xml"));
@@ -248,7 +248,7 @@ class PollRequestFlowTest extends FlowTestCase<PollRequestFlow> {
         new PollMessage.OneTime.Builder()
             .setRegistrarId("NewRegistrar")
             .setMsg("Deleted contact jd1234")
-            .setParent(historyEntry)
+            .setHistoryEntry(historyEntry)
             .setEventTime(clock.nowUtc().minusDays(1))
             .build());
     assertTransactionalFlow(false);
@@ -271,7 +271,7 @@ class PollRequestFlowTest extends FlowTestCase<PollRequestFlow> {
         new PollMessage.OneTime.Builder()
             .setRegistrarId("NewRegistrar")
             .setMsg("Deleted host ns1.test.example")
-            .setParent(historyEntry)
+            .setHistoryEntry(historyEntry)
             .setEventTime(clock.nowUtc().minusDays(1))
             .build());
     clock.advanceOneMilli();

core/src/test/java/google/registry/model/contact/ContactResourceTest.java

@@ -156,7 +156,7 @@ public class ContactResourceTest extends EntityTestCase {
                 originalContact
                     .getTransferData()
                     .asBuilder()
-                    .setServerApproveEntities(null)
+                    .setServerApproveEntities(null, null, null)
                     .build())
             .build();
     assertAboutImmutableObjects().that(persisted).isEqualExceptFields(fixed, "updateTimestamp");

core/src/test/java/google/registry/model/domain/DomainBaseSqlTest.java

@@ -422,14 +422,14 @@ public class DomainBaseSqlTest {
             .setId(300L)
             .setRegistrarId("registrar1")
             .setEventTime(DateTime.now(UTC).plusYears(1))
-            .setParent(historyEntry)
+            .setHistoryEntry(historyEntry)
             .build();
     PollMessage.OneTime deletePollMessage =
         new PollMessage.OneTime.Builder()
             .setId(400L)
             .setRegistrarId("registrar1")
             .setEventTime(DateTime.now(UTC).plusYears(1))
-            .setParent(historyEntry)
+            .setHistoryEntry(historyEntry)
             .build();
     BillingEvent.OneTime oneTimeBillingEvent =
         new BillingEvent.OneTime.Builder()
@@ -469,7 +469,8 @@ public class DomainBaseSqlTest {
         domain
             .asBuilder()
             .setAutorenewBillingEvent(billEvent.createVKey())
-            .setAutorenewPollMessage(autorenewPollMessage.createVKey())
+            .setAutorenewPollMessage(
+                autorenewPollMessage.createVKey(), autorenewPollMessage.getHistoryRevisionId())
             .setDeletePollMessage(deletePollMessage.createVKey())
             .setTransferData(transferData)
             .setGracePeriods(gracePeriods)
@@ -548,14 +549,14 @@ public class DomainBaseSqlTest {
             .setId(300L)
             .setRegistrarId("registrar1")
             .setEventTime(DateTime.now(UTC).plusYears(1))
-            .setParent(historyEntry)
+            .setHistoryEntry(historyEntry)
             .build();
     PollMessage.OneTime deletePollMessage =
         new PollMessage.OneTime.Builder()
             .setId(400L)
             .setRegistrarId("registrar1")
             .setEventTime(DateTime.now(UTC).plusYears(1))
-            .setParent(historyEntry)
+            .setHistoryEntry(historyEntry)
             .build();
     BillingEvent.OneTime oneTimeBillingEvent =
         new BillingEvent.OneTime.Builder()
@@ -572,6 +573,8 @@ public class DomainBaseSqlTest {
             .build();
     DomainTransferData transferData =
         createPendingTransferData(
+            domain.getRepoId(),
+            historyEntry.getId(),
             new DomainTransferData.Builder()
                 .setTransferRequestTrid(Trid.create("foo", "bar"))
                 .setTransferRequestTime(fakeClock.nowUtc())
@@ -601,7 +604,8 @@ public class DomainBaseSqlTest {
             .setAutorenewBillingEvent(
                 createLegacyVKey(BillingEvent.Recurring.class, billEvent.getId()))
             .setAutorenewPollMessage(
-                createLegacyVKey(PollMessage.Autorenew.class, autorenewPollMessage.getId()))
+                createLegacyVKey(PollMessage.Autorenew.class, autorenewPollMessage.getId()),
+                autorenewPollMessage.getHistoryRevisionId())
             .setDeletePollMessage(
                 createLegacyVKey(PollMessage.OneTime.class, deletePollMessage.getId()))
             .setTransferData(transferData)

core/src/test/java/google/registry/model/domain/DomainBaseTest.java

@@ -21,6 +21,7 @@ import static com.google.common.truth.Truth8.assertThat;
 import static google.registry.model.EppResourceUtils.loadByForeignKey;
 import static google.registry.testing.DatabaseHelper.cloneAndSetAutoTimestamps;
 import static google.registry.testing.DatabaseHelper.createTld;
+import static google.registry.testing.DatabaseHelper.insertInDb;
 import static google.registry.testing.DatabaseHelper.newDomainBase;
 import static google.registry.testing.DatabaseHelper.newHostResource;
 import static google.registry.testing.DatabaseHelper.persistActiveContact;
@@ -28,6 +29,7 @@ import static google.registry.testing.DatabaseHelper.persistActiveDomain;
 import static google.registry.testing.DatabaseHelper.persistActiveHost;
 import static google.registry.testing.DatabaseHelper.persistResource;
 import static google.registry.testing.DomainBaseSubject.assertAboutDomains;
+import static google.registry.testing.SqlHelper.saveRegistrar;
 import static google.registry.util.DateTimeUtils.END_OF_TIME;
 import static google.registry.util.DateTimeUtils.START_OF_TIME;
 import static org.joda.money.CurrencyUnit.USD;
@@ -41,7 +43,6 @@ import com.google.common.collect.Iterables;
 import com.google.common.collect.Ordering;
 import com.google.common.collect.Streams;
 import com.googlecode.objectify.Key;
-import google.registry.model.EntityTestCase;
 import google.registry.model.ImmutableObject;
 import google.registry.model.ImmutableObjectSubject;
 import google.registry.model.billing.BillingEvent;
@@ -62,15 +63,28 @@ import google.registry.model.tld.Registry;
 import google.registry.model.transfer.DomainTransferData;
 import google.registry.model.transfer.TransferStatus;
 import google.registry.persistence.VKey;
+import google.registry.testing.AppEngineExtension;
+import google.registry.testing.FakeClock;
 import java.util.Optional;
 import org.joda.money.Money;
 import org.joda.time.DateTime;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
 
 /** Unit tests for {@link DomainBase}. */
 @SuppressWarnings("WeakerAccess") // Referred to by EppInputTest.
-public class DomainBaseTest extends EntityTestCase {
+public class DomainBaseTest {
+
+  protected FakeClock fakeClock = new FakeClock(DateTime.now(UTC));
+
+  @RegisterExtension
+  public final AppEngineExtension appEngine =
+      AppEngineExtension.builder()
+          .withDatastoreAndCloudSql()
+          .enableJpaEntityCoverageCheck(true)
+          .withClock(fakeClock)
+          .build();
 
   private DomainBase domain;
   private VKey<BillingEvent.OneTime> oneTimeBillKey;
@@ -80,6 +94,10 @@ public class DomainBaseTest extends EntityTestCase {
 
   @BeforeEach
   void setUp() {
+    saveRegistrar("registrar1");
+    saveRegistrar("registrar2");
+    saveRegistrar("losing");
+    saveRegistrar("gaining");
     createTld("com");
     domain = persistActiveDomain("example.com");
     VKey<HostResource> hostKey = persistActiveHost("ns1.example.com").createVKey();
@@ -107,19 +125,48 @@ public class DomainBaseTest extends EntityTestCase {
                     .setParent(domainHistory)
                     .build())
             .createVKey();
-    recurringBillKey =
+    DomainHistory historyEntry =
-        persistResource(
+        new DomainHistory.Builder()
-                new BillingEvent.Recurring.Builder()
+            .setId(100L)
-                    .setReason(Reason.RENEW)
+            .setType(HistoryEntry.Type.DOMAIN_CREATE)
-                    .setFlags(ImmutableSet.of(Flag.AUTO_RENEW))
+            .setPeriod(Period.create(1, Period.Unit.YEARS))
-                    .setTargetId(domain.getDomainName())
+            .setModificationTime(DateTime.now(UTC))
-                    .setRegistrarId(domain.getCurrentSponsorRegistrarId())
+            .setDomainRepoId(domain.getRepoId())
-                    .setDomainRepoId(domain.getRepoId())
+            .setRegistrarId(domain.getCurrentSponsorRegistrarId())
-                    .setEventTime(DateTime.now(UTC).plusYears(1))
+            // These are non-null, but I don't think some tests set them.
-                    .setRecurrenceEndTime(END_OF_TIME)
+            .setReason("felt like it")
-                    .setParent(domainHistory)
+            .setRequestedByRegistrar(false)
-                    .build())
+            .setXmlBytes(new byte[0])
-            .createVKey();
+            .build();
+    BillingEvent.OneTime oneTimeBill =
+        new BillingEvent.OneTime.Builder()
+            .setId(500L)
+            // Use SERVER_STATUS so we don't have to add a period.
+            .setReason(Reason.SERVER_STATUS)
+            .setTargetId("example.com")
+            .setRegistrarId("registrar1")
+            .setDomainRepoId("4-COM")
+            .setBillingTime(DateTime.now(UTC))
+            .setCost(Money.of(USD, 100))
+            .setEventTime(DateTime.now(UTC).plusYears(1))
+            .setParent(historyEntry)
+            .build();
+    oneTimeBillKey = oneTimeBill.createVKey();
+    BillingEvent.Recurring recurringBill =
+        new BillingEvent.Recurring.Builder()
+            .setId(200L)
+            .setReason(Reason.RENEW)
+            .setFlags(ImmutableSet.of(Flag.AUTO_RENEW))
+            .setTargetId(domain.getDomainName())
+            .setRegistrarId(domain.getCurrentSponsorRegistrarId())
+            .setDomainRepoId(domain.getRepoId())
+            .setDomainHistoryRevisionId(historyEntry.getId())
+            .setEventTime(DateTime.now(UTC).plusYears(1))
+            .setRecurrenceEndTime(END_OF_TIME)
+            .setParent(historyEntry)
+            .build();
+    insertInDb(historyEntry, oneTimeBill, recurringBill);
+    recurringBillKey = recurringBill.createVKey();
     VKey<PollMessage.Autorenew> autorenewPollKey =
         VKey.from(Key.create(Key.create(domainHistory), PollMessage.Autorenew.class, 3));
     VKey<PollMessage.OneTime> onetimePollKey =
@@ -134,6 +181,7 @@ public class DomainBaseTest extends EntityTestCase {
                     .setCreationRegistrarId("TheRegistrar")
                     .setLastEppUpdateTime(fakeClock.nowUtc())
                     .setLastEppUpdateRegistrarId("NewRegistrar")
+                    .setPersistedCurrentSponsorRegistrarId("NewRegistrar")
                     .setLastTransferTime(fakeClock.nowUtc())
                     .setStatusValues(
                         ImmutableSet.of(
@@ -144,7 +192,6 @@ public class DomainBaseTest extends EntityTestCase {
                             StatusValue.SERVER_RENEW_PROHIBITED,
                             StatusValue.SERVER_HOLD))
                     .setRegistrant(contact1Key)
-                    .setContacts(ImmutableSet.of(DesignatedContact.create(Type.ADMIN, contact2Key)))
                     .setNameservers(ImmutableSet.of(hostKey))
                     .setSubordinateHosts(ImmutableSet.of("ns1.example.com"))
                     .setPersistedCurrentSponsorRegistrarId("NewRegistrar")
@@ -160,6 +207,8 @@ public class DomainBaseTest extends EntityTestCase {
                             .setLosingRegistrarId("NewRegistrar")
                             .setPendingTransferExpirationTime(fakeClock.nowUtc())
                             .setServerApproveEntities(
+                                historyEntry.getDomainRepoId(),
+                                historyEntry.getId(),
                                 ImmutableSet.of(oneTimeBillKey, recurringBillKey, autorenewPollKey))
                             .setServerApproveBillingEvent(oneTimeBillKey)
                             .setServerApproveAutorenewEvent(recurringBillKey)
@@ -170,7 +219,7 @@ public class DomainBaseTest extends EntityTestCase {
                             .build())
                     .setDeletePollMessage(onetimePollKey)
                     .setAutorenewBillingEvent(recurringBillKey)
-                    .setAutorenewPollMessage(autorenewPollKey)
+                    .setAutorenewPollMessage(autorenewPollKey, historyEntry.getId())
                     .setSmdId("smdid")
                     .addGracePeriod(
                         GracePeriod.create(
@@ -200,19 +249,6 @@ public class DomainBaseTest extends EntityTestCase {
         .hasValue(domain);
   }
 
-  @Test
-  void testVKeyRestoration() {
-    assertThat(domain.deletePollMessageHistoryId).isEqualTo(domainHistory.getId());
-    assertThat(domain.autorenewBillingEventHistoryId).isEqualTo(domainHistory.getId());
-    assertThat(domain.autorenewPollMessageHistoryId).isEqualTo(domainHistory.getId());
-    assertThat(domain.getTransferData().getServerApproveBillingEventHistoryId())
-        .isEqualTo(domainHistory.getId());
-    assertThat(domain.getTransferData().getServerApproveAutorenewEventHistoryId())
-        .isEqualTo(domainHistory.getId());
-    assertThat(domain.getTransferData().getServerApproveAutorenewPollMessageHistoryId())
-        .isEqualTo(domainHistory.getId());
-  }
-
   @Test
   void testEmptyStringsBecomeNull() {
     assertThat(
@@ -238,7 +274,6 @@ public class DomainBaseTest extends EntityTestCase {
         .isNotNull();
   }
 
-  @Test
   void testEmptySetsAndArraysBecomeNull() {
     assertThat(
             newDomainBase("example.com")
@@ -407,7 +442,10 @@ public class DomainBaseTest extends EntityTestCase {
                     .setPendingTransferExpirationTime(fakeClock.nowUtc().plusDays(1))
                     .setGainingRegistrarId("TheRegistrar")
                     .setServerApproveBillingEvent(transferBillingEvent.createVKey())
-                    .setServerApproveEntities(ImmutableSet.of(transferBillingEvent.createVKey()))
+                    .setServerApproveEntities(
+                        domain.getRepoId(),
+                        historyEntry.getId(),
+                        ImmutableSet.of(transferBillingEvent.createVKey()))
                     .build())
             .addGracePeriod(
                 // Okay for billing event to be null since the point of this grace period is just

core/src/test/java/google/registry/model/poll/PollMessageExternalKeyConverterTest.java

@@ -83,7 +83,7 @@ public class PollMessageExternalKeyConverterTest {
                 .setRegistrarId("TheRegistrar")
                 .setEventTime(clock.nowUtc())
                 .setMsg("Test poll message")
-                .setParent(historyEntry)
+                .setHistoryEntry(historyEntry)
                 .build());
     assertThat(makePollMessageExternalId(pollMessage)).isEqualTo("1-2-FOOBAR-4-5-2007");
     assertVKeysEqual(parsePollMessageExternalId("1-2-FOOBAR-4-5-2007"), pollMessage.createVKey());
@@ -100,7 +100,7 @@ public class PollMessageExternalKeyConverterTest {
                 .setRegistrarId("TheRegistrar")
                 .setEventTime(clock.nowUtc())
                 .setMsg("Test poll message")
-                .setParent(historyEntry)
+                .setHistoryEntry(historyEntry)
                 .build());
     assertThat(makePollMessageExternalId(pollMessage)).isEqualTo("2-5-ROID-6-7-2007");
     assertVKeysEqual(parsePollMessageExternalId("2-5-ROID-6-7-2007"), pollMessage.createVKey());
@@ -117,7 +117,7 @@ public class PollMessageExternalKeyConverterTest {
                 .setRegistrarId("TheRegistrar")
                 .setEventTime(clock.nowUtc())
                 .setMsg("Test poll message")
-                .setParent(historyEntry)
+                .setHistoryEntry(historyEntry)
                 .build());
     assertThat(makePollMessageExternalId(pollMessage)).isEqualTo("3-5-ROID-6-7-2007");
     assertVKeysEqual(parsePollMessageExternalId("3-5-ROID-6-7-2007"), pollMessage.createVKey());
@@ -170,6 +170,5 @@ public class PollMessageExternalKeyConverterTest {
                 || two.getKind().isAssignableFrom(one.getKind()))
         .isTrue();
     assertThat(one.getSqlKey()).isEqualTo(two.getSqlKey());
-    assertThat(one.getOfyKey()).isEqualTo(two.getOfyKey());
   }
 }

core/src/test/java/google/registry/model/poll/PollMessageTest.java

@@ -80,7 +80,7 @@ public class PollMessageTest extends EntityTestCase {
             .setRegistrarId("TheRegistrar")
             .setEventTime(fakeClock.nowUtc())
             .setMsg("Test poll message")
-            .setParent(historyEntry)
+            .setHistoryEntry(historyEntry)
             .build();
     autoRenew =
         new PollMessage.Autorenew.Builder()
@@ -88,7 +88,7 @@ public class PollMessageTest extends EntityTestCase {
             .setRegistrarId("TheRegistrar")
             .setEventTime(fakeClock.nowUtc())
             .setMsg("Test poll message")
-            .setParent(historyEntry)
+            .setHistoryEntry(historyEntry)
             .setAutorenewEndTime(fakeClock.nowUtc().plusDays(365))
             .setTargetId("foobar.foo")
             .build();
@@ -116,7 +116,7 @@ public class PollMessageTest extends EntityTestCase {
                 .setRegistrarId("TheRegistrar")
                 .setEventTime(fakeClock.nowUtc())
                 .setMsg("Test poll message")
-                .setParent(historyEntry)
+                .setHistoryEntry(historyEntry)
                 .build());
     assertThat(tm().transact(() -> tm().loadByEntity(pollMessage))).isEqualTo(pollMessage);
   }
@@ -135,16 +135,15 @@ public class PollMessageTest extends EntityTestCase {
             .setRegistrarId("TheRegistrar")
             .setEventTime(fakeClock.nowUtc())
             .setMsg("Test poll message")
-            .setParent(historyEntry)
+            .setHistoryEntry(historyEntry)
             .setResponseData(ImmutableList.of(hostPendingActionNotificationResponse))
             .build();
     persistResource(pollMessage);
     assertThat(tm().transact(() -> tm().loadByEntity(pollMessage).getMsg()))
         .isEqualTo(pollMessage.msg);
     assertThat(
-            tm().transact(() -> tm().loadByEntity(pollMessage))
+            tm().transact(() -> tm().loadByEntity(pollMessage)).pendingActionNotificationResponse)
-                .hostPendingActionNotificationResponses)
+        .isEqualTo(hostPendingActionNotificationResponse);
-        .contains(hostPendingActionNotificationResponse);
   }
 
   @TestSqlOnly
@@ -155,7 +154,7 @@ public class PollMessageTest extends EntityTestCase {
                 .setRegistrarId("TheRegistrar")
                 .setEventTime(fakeClock.nowUtc())
                 .setMsg("Test poll message")
-                .setParent(historyEntry)
+                .setHistoryEntry(historyEntry)
                 .build());
     PollMessage persisted = tm().transact(() -> tm().loadByEntity(pollMessage));
     assertThat(SerializeUtils.serializeDeserialize(persisted)).isEqualTo(persisted);
@@ -169,7 +168,7 @@ public class PollMessageTest extends EntityTestCase {
                 .setRegistrarId("TheRegistrar")
                 .setEventTime(fakeClock.nowUtc())
                 .setMsg("Test poll message")
-                .setParent(historyEntry)
+                .setHistoryEntry(historyEntry)
                 .setAutorenewEndTime(fakeClock.nowUtc().plusDays(365))
                 .setTargetId("foobar.foo")
                 .build());
@@ -184,7 +183,7 @@ public class PollMessageTest extends EntityTestCase {
                 .setRegistrarId("TheRegistrar")
                 .setEventTime(fakeClock.nowUtc())
                 .setMsg("Test poll message")
-                .setParent(historyEntry)
+                .setHistoryEntry(historyEntry)
                 .setAutorenewEndTime(fakeClock.nowUtc().plusDays(365))
                 .setTargetId("foobar.foo")
                 .build());
@@ -200,7 +199,7 @@ public class PollMessageTest extends EntityTestCase {
                 .setRegistrarId("TheRegistrar")
                 .setEventTime(fakeClock.nowUtc())
                 .setMsg("Test poll message")
-                .setParent(historyEntry)
+                .setHistoryEntry(historyEntry)
                 .setAutorenewEndTime(fakeClock.nowUtc().plusDays(365))
                 .setTargetId("foobar.foo")
                 .build());

core/src/test/java/google/registry/model/transfer/TransferDataTest.java

@@ -95,6 +95,8 @@ public class TransferDataTest {
             .setPendingTransferExpirationTime(now)
             .setTransferStatus(TransferStatus.PENDING)
             .setServerApproveEntities(
+                "4-TLD",
+                1356L,
                 ImmutableSet.of(
                     transferBillingEventKey,
                     otherServerApproveBillingEventKey,

core/src/test/java/google/registry/persistence/DomainHistoryVKeyTest.java

@@ -55,17 +55,10 @@ class DomainHistoryVKeyTest {
     TestEntity persisted = tm().transact(() -> tm().loadByKey(original.createVKey()));
     assertThat(persisted).isEqualTo(original);
     // Double check that the persisted.domainHistoryVKey is a symmetric VKey
-    assertThat(persisted.domainHistoryVKey.createOfyKey())
-        .isEqualTo(
-            Key.create(Key.create(DomainBase.class, "domainRepoId"), HistoryEntry.class, 10L));
     assertThat(persisted.domainHistoryVKey.createSqlKey())
         .isEqualTo(new DomainHistoryId("domainRepoId", 10L));
     assertThat(persisted.domainHistoryVKey.createVKey())
-        .isEqualTo(
+        .isEqualTo(VKey.createSql(HistoryEntry.class, new DomainHistoryId("domainRepoId", 10L)));
-            VKey.create(
-                HistoryEntry.class,
-                new DomainHistoryId("domainRepoId", 10L),
-                Key.create(Key.create(DomainBase.class, "domainRepoId"), HistoryEntry.class, 10L)));
   }
 
   @TestOfyAndSql
@@ -73,7 +66,6 @@ class DomainHistoryVKeyTest {
     Key<HistoryEntry> ofyKey =
         Key.create(Key.create(DomainBase.class, "domainRepoId"), HistoryEntry.class, 10L);
     DomainHistoryVKey domainHistoryVKey = DomainHistoryVKey.create(ofyKey);
-    assertThat(domainHistoryVKey.createOfyKey()).isEqualTo(ofyKey);
     assertThat(domainHistoryVKey.createSqlKey())
         .isEqualTo(new DomainHistoryId("domainRepoId", 10L));
     assertThat(domainHistoryVKey.createVKey())

core/src/test/java/google/registry/rde/DomainBaseToXjcConverterTest.java

@@ -333,9 +333,10 @@ public class DomainBaseToXjcConverterTest {
                             .setEventTime(END_OF_TIME)
                             .setAutorenewEndTime(END_OF_TIME)
                             .setMsg("Domain was auto-renewed.")
-                            .setParent(domainHistory)
+                            .setHistoryEntry(domainHistory)
                             .build())
-                    .createVKey())
+                    .createVKey(),
+                domainHistory.getId())
             .setTransferData(
                 new DomainTransferData.Builder()
                     .setGainingRegistrarId("NewRegistrar")
@@ -362,10 +363,13 @@ public class DomainBaseToXjcConverterTest {
                                     .setEventTime(END_OF_TIME)
                                     .setAutorenewEndTime(END_OF_TIME)
                                     .setMsg("Domain was auto-renewed.")
-                                    .setParent(domainHistory)
+                                    .setHistoryEntry(domainHistory)
                                     .build())
                             .createVKey())
-                    .setServerApproveEntities(ImmutableSet.of(billingEvent.createVKey()))
+                    .setServerApproveEntities(
+                        domain.getRepoId(),
+                        domainHistory.getId(),
+                        ImmutableSet.of(billingEvent.createVKey()))
                     .setTransferRequestTime(DateTime.parse("1919-01-01T00:00:00Z"))
                     .setTransferStatus(TransferStatus.PENDING)
                     .setTransferredRegistrationExpirationTime(

core/src/test/java/google/registry/rde/RdeFixtures.java

@@ -174,9 +174,10 @@ final class RdeFixtures {
                             .setEventTime(END_OF_TIME)
                             .setAutorenewEndTime(END_OF_TIME)
                             .setMsg("Domain was auto-renewed.")
-                            .setParent(historyEntry)
+                            .setHistoryEntry(historyEntry)
                             .build())
-                    .createVKey())
+                    .createVKey(),
+                historyEntry.getId())
             .setTransferData(
                 new DomainTransferData.Builder()
                     .setGainingRegistrarId("gaining")
@@ -203,10 +204,13 @@ final class RdeFixtures {
                                     .setEventTime(END_OF_TIME)
                                     .setAutorenewEndTime(END_OF_TIME)
                                     .setMsg("Domain was auto-renewed.")
-                                    .setParent(historyEntry)
+                                    .setHistoryEntry(historyEntry)
                                     .build())
                             .createVKey())
-                    .setServerApproveEntities(ImmutableSet.of(billingEvent.createVKey()))
+                    .setServerApproveEntities(
+                        historyEntry.getDomainRepoId(),
+                        historyEntry.getId(),
+                        ImmutableSet.of(billingEvent.createVKey()))
                     .setTransferRequestTime(DateTime.parse("1991-01-01T00:00:00Z"))
                     .setTransferStatus(TransferStatus.PENDING)
                     .setTransferredRegistrationExpirationTime(

core/src/test/java/google/registry/testing/DatabaseHelper.java

@@ -510,7 +510,7 @@ public class DatabaseHelper {
         .setEventTime(expirationTime)
         .setMsg("Transfer server approved.")
         .setResponseData(ImmutableList.of(createTransferResponse(resource, transferData)))
-        .setParent(historyEntry)
+        .setHistoryEntry(historyEntry)
         .build();
   }
 
@@ -549,6 +549,8 @@ public class DatabaseHelper {
                 createContactTransferDataBuilder(requestTime, expirationTime)
                     .setPendingTransferExpirationTime(now.plus(getContactAutomaticTransferLength()))
                     .setServerApproveEntities(
+                        ((ContactHistory) historyEntryContactTransfer).getContactRepoId(),
+                        historyEntryContactTransfer.getId(),
                         ImmutableSet.of(
                             // Pretend it's 3 days since the request
                             persistResource(
@@ -630,13 +632,14 @@ public class DatabaseHelper {
                 .setEventTime(expirationTime)
                 .setAutorenewEndTime(END_OF_TIME)
                 .setMsg("Domain was auto-renewed.")
-                .setParent(historyEntryDomainCreate)
+                .setHistoryEntry(historyEntryDomainCreate)
                 .build());
     return persistResource(
         domain
             .asBuilder()
             .setAutorenewBillingEvent(autorenewEvent.createVKey())
-            .setAutorenewPollMessage(autorenewPollMessage.createVKey())
+            .setAutorenewPollMessage(
+                autorenewPollMessage.createVKey(), autorenewPollMessage.getHistoryRevisionId())
             .build());
   }
 
@@ -676,7 +679,7 @@ public class DatabaseHelper {
                 .setEventTime(extendedRegistrationExpirationTime)
                 .setAutorenewEndTime(END_OF_TIME)
                 .setMsg("Domain was auto-renewed.")
-                .setParent(historyEntryDomainTransfer)
+                .setHistoryEntry(historyEntryDomainTransfer)
                 .build());
     // Modify the existing autorenew event to reflect the pending transfer.
     persistResource(
@@ -711,6 +714,8 @@ public class DatabaseHelper {
                     .setServerApproveAutorenewPollMessage(
                         gainingClientAutorenewPollMessage.createVKey())
                     .setServerApproveEntities(
+                        historyEntryDomainTransfer.getDomainRepoId(),
+                        historyEntryDomainTransfer.getId(),
                         ImmutableSet.of(
                             transferBillingEvent.createVKey(),
                             gainingClientAutorenewEvent.createVKey(),
@@ -887,9 +892,7 @@ public class DatabaseHelper {
     return transactIfJpaTm(
         () ->
             tm().loadAllOf(PollMessage.class).stream()
-                .filter(
+                .filter(pollMessage -> pollMessage.getDomainRepoId().equals(domain.getRepoId()))
-                    pollMessage ->
-                        pollMessage.getParentKey().getParent().getName().equals(domain.getRepoId()))
                 .collect(toImmutableList()));
   }
 
@@ -909,13 +912,7 @@ public class DatabaseHelper {
     return transactIfJpaTm(
         () ->
             tm().loadAllOf(PollMessage.class).stream()
-                .filter(
+                .filter(pollMessage -> pollMessage.getDomainRepoId().equals(resource.getRepoId()))
-                    pollMessage ->
-                        pollMessage
-                            .getParentKey()
-                            .getParent()
-                            .getName()
-                            .equals(resource.getRepoId()))
                 .filter(pollMessage -> pollMessage.getRegistrarId().equals(registrarId))
                 .filter(
                     pollMessage ->
@@ -1176,7 +1173,14 @@ public class DatabaseHelper {
             () ->
                 tm().loadAllOf(PollMessage.class).stream()
                     .filter(
-                        pollMessage -> pollMessage.getParentKey().equals(Key.create(historyEntry)))
+                        pollMessage ->
+                            pollMessage.getResourceName().equals(historyEntry.getParent().getName())
+                                && pollMessage.getHistoryRevisionId() == historyEntry.getId()
+                                && pollMessage
+                                    .getType()
+                                    .getResourceClass()
+                                    .getName()
+                                    .equals(historyEntry.getParent().getKind()))
                     .collect(toImmutableList())));
   }
 

core/src/test/java/google/registry/tools/AckPollMessagesCommandTest.java

@@ -23,9 +23,9 @@ import static google.registry.testing.DatabaseHelper.newDomainBase;
 import static google.registry.testing.DatabaseHelper.persistResource;
 
 import com.google.common.collect.ImmutableList;
-import com.googlecode.objectify.Key;
 import google.registry.model.domain.DomainBase;
 import google.registry.model.domain.DomainHistory;
+import google.registry.model.domain.DomainHistory.DomainHistoryId;
 import google.registry.model.ofy.Ofy;
 import google.registry.model.poll.PollMessage;
 import google.registry.model.poll.PollMessage.Autorenew;
@@ -100,7 +100,7 @@ public class AckPollMessagesCommandTest extends CommandTestCase<AckPollMessagesC
         persistResource(
             new PollMessage.Autorenew.Builder()
                 .setId(625L)
-                .setParentKey(domainHistory.createVKey().getOfyKey())
+                .setHistoryEntry(domainHistory)
                 .setEventTime(DateTime.parse("2011-04-15T22:33:44Z"))
                 .setRegistrarId("TheRegistrar")
                 .setMsg("autorenew")
@@ -127,7 +127,7 @@ public class AckPollMessagesCommandTest extends CommandTestCase<AckPollMessagesC
         persistResource(
             new PollMessage.Autorenew.Builder()
                 .setId(625L)
-                .setParentKey(domainHistory.createVKey().getOfyKey())
+                .setHistoryEntry(domainHistory)
                 .setEventTime(DateTime.parse("2011-04-15T22:33:44Z"))
                 .setAutorenewEndTime(DateTime.parse("2012-01-01T22:33:44Z"))
                 .setRegistrarId("TheRegistrar")
@@ -172,7 +172,7 @@ public class AckPollMessagesCommandTest extends CommandTestCase<AckPollMessagesC
         persistResource(
             new PollMessage.OneTime.Builder()
                 .setId(2474L)
-                .setParentKey(domainHistory.createVKey().getOfyKey())
+                .setHistoryEntry(domainHistory)
                 .setRegistrarId("NewRegistrar")
                 .setEventTime(DateTime.parse("2013-06-01T22:33:44Z"))
                 .setMsg("baaaahh")
@@ -202,11 +202,7 @@ public class AckPollMessagesCommandTest extends CommandTestCase<AckPollMessagesC
     return persistResource(
         new PollMessage.OneTime.Builder()
             .setId(id)
-            .setParentKey(
+            .setDomainHistoryId(new DomainHistoryId("FSDGS-TLD", domainHistory.getId()))
-                Key.create(
-                    Key.create(DomainBase.class, "FSDGS-TLD"),
-                    HistoryEntry.class,
-                    domainHistory.getId()))
             .setRegistrarId("TheRegistrar")
             .setEventTime(eventTime)
             .setMsg(message)

core/src/test/java/google/registry/tools/EnqueuePollMessageCommandTest.java

@@ -75,7 +75,7 @@ class EnqueuePollMessageCommandTest extends CommandTestCase<EnqueuePollMessageCo
     assertPollMessages(
         "TheRegistrar",
         new PollMessage.OneTime.Builder()
-            .setParent(synthetic)
+            .setHistoryEntry(synthetic)
             .setMsg("This domain is bad")
             .setRegistrarId("TheRegistrar")
             .setEventTime(fakeClock.nowUtc())
@@ -107,7 +107,7 @@ class EnqueuePollMessageCommandTest extends CommandTestCase<EnqueuePollMessageCo
     assertPollMessages(
         "TheRegistrar",
         new PollMessage.OneTime.Builder()
-            .setParent(synthetic)
+            .setHistoryEntry(synthetic)
             .setMsg("This domain needs work")
             .setRegistrarId("TheRegistrar")
             .setEventTime(fakeClock.nowUtc())
@@ -115,7 +115,7 @@ class EnqueuePollMessageCommandTest extends CommandTestCase<EnqueuePollMessageCo
     assertPollMessages(
         "NewRegistrar",
         new PollMessage.OneTime.Builder()
-            .setParent(synthetic)
+            .setHistoryEntry(synthetic)
             .setMsg("This domain needs work")
             .setRegistrarId("NewRegistrar")
             .setEventTime(fakeClock.nowUtc())
@@ -123,7 +123,7 @@ class EnqueuePollMessageCommandTest extends CommandTestCase<EnqueuePollMessageCo
     assertPollMessages(
         "foobaz",
         new PollMessage.OneTime.Builder()
-            .setParent(synthetic)
+            .setHistoryEntry(synthetic)
             .setMsg("This domain needs work")
             .setRegistrarId("foobaz")
             .setEventTime(fakeClock.nowUtc())
@@ -152,7 +152,7 @@ class EnqueuePollMessageCommandTest extends CommandTestCase<EnqueuePollMessageCo
     assertPollMessages(
         "TheRegistrar",
         new PollMessage.OneTime.Builder()
-            .setParent(synthetic)
+            .setHistoryEntry(synthetic)
             .setMsg("This domain needs work")
             .setRegistrarId("TheRegistrar")
             .setEventTime(fakeClock.nowUtc())
@@ -160,7 +160,7 @@ class EnqueuePollMessageCommandTest extends CommandTestCase<EnqueuePollMessageCo
     assertPollMessages(
         "NewRegistrar",
         new PollMessage.OneTime.Builder()
-            .setParent(synthetic)
+            .setHistoryEntry(synthetic)
             .setMsg("This domain needs work")
             .setRegistrarId("NewRegistrar")
             .setEventTime(fakeClock.nowUtc())
@@ -168,7 +168,7 @@ class EnqueuePollMessageCommandTest extends CommandTestCase<EnqueuePollMessageCo
     assertPollMessages(
         "foobaz",
         new PollMessage.OneTime.Builder()
-            .setParent(synthetic)
+            .setHistoryEntry(synthetic)
             .setMsg("This domain needs work")
             .setRegistrarId("foobaz")
             .setEventTime(fakeClock.nowUtc())

core/src/test/java/google/registry/tools/GetDomainCommandTest.java

@@ -38,7 +38,7 @@ class GetDomainCommandTest extends CommandTestCase<GetDomainCommand> {
     persistActiveDomain("example.tld");
     runCommand("example.tld");
     assertInStdout("fullyQualifiedDomainName=example.tld");
-    assertInStdout("contact=Key<?>(ContactResource(\"3-ROID\"))");
+    assertInStdout("Contact=VKey<ContactResource>(sql:3-ROID");
     assertInStdout(
         "Websafe key: "
             + "kind:DomainBase"
@@ -51,7 +51,7 @@ class GetDomainCommandTest extends CommandTestCase<GetDomainCommand> {
     persistActiveDomain("example.tld");
     runCommand("example.tld", "--expand");
     assertInStdout("fullyQualifiedDomainName=example.tld");
-    assertInStdout("contact=Key<?>(ContactResource(\"3-ROID\"))");
+    assertInStdout("sqlKey=3-ROID");
     assertInStdout(
         "Websafe key: "
             + "kind:DomainBase"
@@ -66,7 +66,7 @@ class GetDomainCommandTest extends CommandTestCase<GetDomainCommand> {
     persistActiveDomain("xn--aualito-txac.xn--q9jyb4c");
     runCommand("çauçalito.みんな", "--expand");
     assertInStdout("fullyQualifiedDomainName=xn--aualito-txac.xn--q9jyb4c");
-    assertInStdout("contact=Key<?>(ContactResource(\"4-ROID\"))");
+    assertInStdout("sqlKey=4-ROID");
   }
 
   @Test

core/src/test/java/google/registry/tools/UnrenewDomainCommandTest.java

@@ -35,7 +35,6 @@ import static google.registry.testing.HistoryEntrySubject.assertAboutHistoryEntr
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
 import com.google.common.collect.ImmutableSet;
-import com.googlecode.objectify.Key;
 import google.registry.model.billing.BillingEvent;
 import google.registry.model.billing.BillingEvent.Flag;
 import google.registry.model.billing.BillingEvent.Reason;
@@ -148,7 +147,7 @@ public class UnrenewDomainCommandTest extends CommandTestCase<UnrenewDomainComma
         getPollMessages(domain),
         ImmutableSet.of(
             new PollMessage.OneTime.Builder()
-                .setParent(synthetic)
+                .setHistoryEntry(synthetic)
                 .setRegistrarId("TheRegistrar")
                 .setMsg(
                     "Domain foo.tld was unrenewed by 2 years; "
@@ -156,7 +155,7 @@ public class UnrenewDomainCommandTest extends CommandTestCase<UnrenewDomainComma
                 .setEventTime(unrenewTime)
                 .build(),
             new PollMessage.Autorenew.Builder()
-                .setParent(synthetic)
+                .setHistoryEntry(synthetic)
                 .setTargetId("foo.tld")
                 .setRegistrarId("TheRegistrar")
                 .setEventTime(newExpirationTime)
@@ -164,8 +163,7 @@ public class UnrenewDomainCommandTest extends CommandTestCase<UnrenewDomainComma
                 .build()));
 
     // Check that fields on domain were updated correctly.
-    assertThat(domain.getAutorenewPollMessage().getOfyKey().getParent())
+    assertThat(domain.getAutorenewPollMessageHistoryId()).isEqualTo(synthetic.getId());
-        .isEqualTo(Key.create(synthetic));
     assertThat(domain.getRegistrationExpirationTime()).isEqualTo(newExpirationTime);
     assertThat(domain.getLastEppUpdateTime()).isEqualTo(unrenewTime);
     assertThat(domain.getLastEppUpdateRegistrarId()).isEqualTo("TheRegistrar");

core/src/test/resources/google/registry/model/schema.txt

@@ -186,16 +186,6 @@ enum google.registry.model.contact.PostalInfo$Type {
   INTERNATIONALIZED;
   LOCALIZED;
 }
-class google.registry.model.domain.DesignatedContact {
-  com.googlecode.objectify.Key<google.registry.model.contact.ContactResource> contact;
-  google.registry.model.domain.DesignatedContact$Type type;
-}
-enum google.registry.model.domain.DesignatedContact$Type {
-  ADMIN;
-  BILLING;
-  REGISTRANT;
-  TECH;
-}
 class google.registry.model.domain.DomainAuthInfo {
   google.registry.model.eppcommon.AuthInfo$PasswordAuth pw;
 }
@@ -207,6 +197,10 @@ class google.registry.model.domain.DomainBase {
   google.registry.model.domain.launch.LaunchNotice launchNotice;
   google.registry.model.transfer.DomainTransferData transferData;
   google.registry.persistence.VKey<google.registry.model.billing.BillingEvent$Recurring> autorenewBillingEvent;
+  google.registry.persistence.VKey<google.registry.model.contact.ContactResource> adminContact;
+  google.registry.persistence.VKey<google.registry.model.contact.ContactResource> billingContact;
+  google.registry.persistence.VKey<google.registry.model.contact.ContactResource> registrantContact;
+  google.registry.persistence.VKey<google.registry.model.contact.ContactResource> techContact;
   google.registry.persistence.VKey<google.registry.model.poll.PollMessage$Autorenew> autorenewPollMessage;
   google.registry.persistence.VKey<google.registry.model.poll.PollMessage$OneTime> deletePollMessage;
   java.lang.String creationClientId;
@@ -216,7 +210,6 @@ class google.registry.model.domain.DomainBase {
   java.lang.String lastEppUpdateClientId;
   java.lang.String smdId;
   java.lang.String tld;
-  java.util.Set<google.registry.model.domain.DesignatedContact> allContacts;
   java.util.Set<google.registry.model.domain.GracePeriod> gracePeriods;
   java.util.Set<google.registry.model.domain.secdns.DelegationSignerData> dsData;
   java.util.Set<google.registry.model.eppcommon.StatusValue> status;
@@ -236,6 +229,10 @@ class google.registry.model.domain.DomainContent {
   google.registry.model.domain.launch.LaunchNotice launchNotice;
   google.registry.model.transfer.DomainTransferData transferData;
   google.registry.persistence.VKey<google.registry.model.billing.BillingEvent$Recurring> autorenewBillingEvent;
+  google.registry.persistence.VKey<google.registry.model.contact.ContactResource> adminContact;
+  google.registry.persistence.VKey<google.registry.model.contact.ContactResource> billingContact;
+  google.registry.persistence.VKey<google.registry.model.contact.ContactResource> registrantContact;
+  google.registry.persistence.VKey<google.registry.model.contact.ContactResource> techContact;
   google.registry.persistence.VKey<google.registry.model.poll.PollMessage$Autorenew> autorenewPollMessage;
   google.registry.persistence.VKey<google.registry.model.poll.PollMessage$OneTime> deletePollMessage;
   java.lang.String creationClientId;
@@ -245,7 +242,6 @@ class google.registry.model.domain.DomainContent {
   java.lang.String lastEppUpdateClientId;
   java.lang.String smdId;
   java.lang.String tld;
-  java.util.Set<google.registry.model.domain.DesignatedContact> allContacts;
   java.util.Set<google.registry.model.domain.GracePeriod> gracePeriods;
   java.util.Set<google.registry.model.domain.secdns.DelegationSignerData> dsData;
   java.util.Set<google.registry.model.eppcommon.StatusValue> status;
@@ -278,16 +274,16 @@ class google.registry.model.domain.DomainHistory {
 }
 class google.registry.model.domain.GracePeriod {
   google.registry.model.domain.rgp.GracePeriodStatus type;
-  google.registry.persistence.BillingVKey$BillingEventVKey billingEventOneTime;
+  google.registry.persistence.VKey<google.registry.model.billing.BillingEvent$OneTime> billingEventOneTime;
-  google.registry.persistence.BillingVKey$BillingRecurrenceVKey billingEventRecurring;
+  google.registry.persistence.VKey<google.registry.model.billing.BillingEvent$Recurring> billingEventRecurring;
   java.lang.String clientId;
   long gracePeriodId;
   org.joda.time.DateTime expirationTime;
 }
 class google.registry.model.domain.GracePeriod$GracePeriodHistory {
   google.registry.model.domain.rgp.GracePeriodStatus type;
-  google.registry.persistence.BillingVKey$BillingEventVKey billingEventOneTime;
+  google.registry.persistence.VKey<google.registry.model.billing.BillingEvent$OneTime> billingEventOneTime;
-  google.registry.persistence.BillingVKey$BillingRecurrenceVKey billingEventRecurring;
+  google.registry.persistence.VKey<google.registry.model.billing.BillingEvent$Recurring> billingEventRecurring;
   java.lang.Long domainHistoryRevisionId;
   java.lang.Long gracePeriodHistoryRevisionId;
   java.lang.String clientId;
@@ -469,35 +465,14 @@ class google.registry.model.index.ForeignKeyIndex$ForeignKeyHostIndex {
   google.registry.persistence.VKey<E> topReference;
   org.joda.time.DateTime deletionTime;
 }
-class google.registry.model.poll.PendingActionNotificationResponse$ContactPendingActionNotificationResponse {
-  google.registry.model.eppcommon.Trid trid;
-  google.registry.model.poll.PendingActionNotificationResponse$NameOrId nameOrId;
-  org.joda.time.DateTime processedDate;
-}
-class google.registry.model.poll.PendingActionNotificationResponse$DomainPendingActionNotificationResponse {
-  google.registry.model.eppcommon.Trid trid;
-  google.registry.model.poll.PendingActionNotificationResponse$NameOrId nameOrId;
-  org.joda.time.DateTime processedDate;
-}
-class google.registry.model.poll.PendingActionNotificationResponse$HostPendingActionNotificationResponse {
-  google.registry.model.eppcommon.Trid trid;
-  google.registry.model.poll.PendingActionNotificationResponse$NameOrId nameOrId;
-  org.joda.time.DateTime processedDate;
-}
-class google.registry.model.poll.PendingActionNotificationResponse$NameOrId {
-  boolean actionResult;
-  java.lang.String value;
-}
 class google.registry.model.poll.PollMessage {
   @Id java.lang.Long id;
-  @Parent com.googlecode.objectify.Key<? extends google.registry.model.reporting.HistoryEntry> parent;
   java.lang.String clientId;
   java.lang.String msg;
   org.joda.time.DateTime eventTime;
 }
 class google.registry.model.poll.PollMessage$Autorenew {
   @Id java.lang.Long id;
-  @Parent com.googlecode.objectify.Key<? extends google.registry.model.reporting.HistoryEntry> parent;
   java.lang.String clientId;
   java.lang.String msg;
   java.lang.String targetId;
@@ -506,14 +481,8 @@ class google.registry.model.poll.PollMessage$Autorenew {
 }
 class google.registry.model.poll.PollMessage$OneTime {
   @Id java.lang.Long id;
-  @Parent com.googlecode.objectify.Key<? extends google.registry.model.reporting.HistoryEntry> parent;
   java.lang.String clientId;
   java.lang.String msg;
-  java.util.List<google.registry.model.poll.PendingActionNotificationResponse$ContactPendingActionNotificationResponse> contactPendingActionNotificationResponses;
-  java.util.List<google.registry.model.poll.PendingActionNotificationResponse$DomainPendingActionNotificationResponse> domainPendingActionNotificationResponses;
-  java.util.List<google.registry.model.poll.PendingActionNotificationResponse$HostPendingActionNotificationResponse> hostPendingActionNotificationResponses;
-  java.util.List<google.registry.model.transfer.TransferResponse$ContactTransferResponse> contactTransferResponses;
-  java.util.List<google.registry.model.transfer.TransferResponse$DomainTransferResponse> domainTransferResponses;
   org.joda.time.DateTime eventTime;
 }
 class google.registry.model.rde.RdeRevision {
@@ -745,7 +714,6 @@ class google.registry.model.transfer.ContactTransferData {
   google.registry.model.transfer.TransferStatus transferStatus;
   java.lang.String gainingClientId;
   java.lang.String losingClientId;
-  java.util.Set<google.registry.persistence.VKey<? extends google.registry.model.transfer.TransferData$TransferServerApproveEntity>> serverApproveEntities;
   org.joda.time.DateTime pendingTransferExpirationTime;
   org.joda.time.DateTime transferRequestTime;
 }
@@ -758,28 +726,10 @@ class google.registry.model.transfer.DomainTransferData {
   google.registry.persistence.VKey<google.registry.model.poll.PollMessage$Autorenew> serverApproveAutorenewPollMessage;
   java.lang.String gainingClientId;
   java.lang.String losingClientId;
-  java.util.Set<google.registry.persistence.VKey<? extends google.registry.model.transfer.TransferData$TransferServerApproveEntity>> serverApproveEntities;
   org.joda.time.DateTime pendingTransferExpirationTime;
   org.joda.time.DateTime transferRequestTime;
   org.joda.time.DateTime transferredRegistrationExpirationTime;
 }
-class google.registry.model.transfer.TransferResponse$ContactTransferResponse {
-  google.registry.model.transfer.TransferStatus transferStatus;
-  java.lang.String contactId;
-  java.lang.String gainingClientId;
-  java.lang.String losingClientId;
-  org.joda.time.DateTime pendingTransferExpirationTime;
-  org.joda.time.DateTime transferRequestTime;
-}
-class google.registry.model.transfer.TransferResponse$DomainTransferResponse {
-  google.registry.model.transfer.TransferStatus transferStatus;
-  java.lang.String fullyQualifiedDomainName;
-  java.lang.String gainingClientId;
-  java.lang.String losingClientId;
-  org.joda.time.DateTime extendedRegistrationExpirationTime;
-  org.joda.time.DateTime pendingTransferExpirationTime;
-  org.joda.time.DateTime transferRequestTime;
-}
 enum google.registry.model.transfer.TransferStatus {
   CLIENT_APPROVED;
   CLIENT_CANCELLED;

db/src/main/resources/sql/schema/db-schema.sql.generated

@@ -265,13 +265,11 @@
         auth_info_repo_id text,
         auth_info_value text,
         billing_recurrence_id int8,
-        billing_recurrence_history_id int8,
         autorenew_end_time timestamptz,
         autorenew_poll_message_id int8,
         autorenew_poll_message_history_id int8,
         billing_contact text,
         deletion_poll_message_id int8,
-        deletion_poll_message_history_id int8,
         dns_refresh_request_time timestamptz,
         domain_name text,
         idn_table_name text,
@@ -286,14 +284,11 @@
         subordinate_hosts text[],
         tech_contact text,
         tld text,
-        transfer_billing_cancellation_history_id int8,
         transfer_billing_cancellation_id int8,
         transfer_billing_recurrence_id int8,
-        transfer_billing_recurrence_history_id int8,
         transfer_autorenew_poll_message_id int8,
         transfer_autorenew_poll_message_history_id int8,
         transfer_billing_event_id int8,
-        transfer_billing_event_history_id int8,
         transfer_renew_period_unit text,
         transfer_renew_period_value int4,
         transfer_registration_expiration_time timestamptz,
@@ -339,13 +334,11 @@
         auth_info_repo_id text,
         auth_info_value text,
         billing_recurrence_id int8,
-        billing_recurrence_history_id int8,
         autorenew_end_time timestamptz,
         autorenew_poll_message_id int8,
         autorenew_poll_message_history_id int8,
         billing_contact text,
         deletion_poll_message_id int8,
-        deletion_poll_message_history_id int8,
         dns_refresh_request_time timestamptz,
         domain_name text,
         idn_table_name text,
@@ -360,14 +353,11 @@
         subordinate_hosts text[],
         tech_contact text,
         tld text,
-        transfer_billing_cancellation_history_id int8,
         transfer_billing_cancellation_id int8,
         transfer_billing_recurrence_id int8,
-        transfer_billing_recurrence_history_id int8,
         transfer_autorenew_poll_message_id int8,
         transfer_autorenew_poll_message_history_id int8,
         transfer_billing_event_id int8,
-        transfer_billing_event_history_id int8,
         transfer_renew_period_unit text,
         transfer_renew_period_value int4,
         transfer_registration_expiration_time timestamptz,
@@ -422,11 +412,7 @@
     create table "GracePeriod" (
        grace_period_id int8 not null,
         billing_event_id int8,
-        billing_event_history_id int8,
-        billing_event_domain_repo_id text,
         billing_recurrence_id int8,
-        billing_recurrence_history_id int8,
-        billing_recurrence_domain_repo_id text,
         registrar_id text not null,
         domain_repo_id text not null,
         expiration_time timestamptz not null,
@@ -437,11 +423,7 @@
     create table "GracePeriodHistory" (
        grace_period_history_revision_id int8 not null,
         billing_event_id int8,
-        billing_event_history_id int8,
-        billing_event_domain_repo_id text,
         billing_recurrence_id int8,
-        billing_recurrence_history_id int8,
-        billing_recurrence_domain_repo_id text,
         registrar_id text not null,
         domain_repo_id text not null,
         expiration_time timestamptz not null,

util/src/main/java/google/registry/util/NullIgnoringCollectionBuilder.java

@@ -0,0 +1,50 @@
+// Copyright 2022 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.util;
+
+import com.google.common.collect.ImmutableCollection;
+import javax.annotation.Nullable;
+
+/**
+ * Collection builder that simply ignores requests to add null elements.
+ *
+ * <p>Useful because we do this in a number of cases.
+ */
+public class NullIgnoringCollectionBuilder<E, B extends ImmutableCollection.Builder<E>> {
+
+  private B builder;
+
+  private NullIgnoringCollectionBuilder(B builder) {
+    this.builder = builder;
+  }
+
+  public static <E2, B2 extends ImmutableCollection.Builder<E2>>
+      NullIgnoringCollectionBuilder<E2, B2> create(B2 builder) {
+    return new NullIgnoringCollectionBuilder<E2, B2>(builder);
+  }
+
+  /** If 'elem' is not null, add it to the builder. */
+  public NullIgnoringCollectionBuilder<E, B> add(@Nullable E elem) {
+    if (elem != null) {
+      builder.add(elem);
+    }
+    return this;
+  }
+
+  /** Returns the underlying builder. */
+  public B getBuilder() {
+    return builder;
+  }
+}

util/src/test/java/google/registry/util/NullIgnoringCollectionBuilderTest.java

@@ -0,0 +1,54 @@
+// Copyright 2022 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.util;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
+import org.junit.jupiter.api.Test;
+
+public class NullIgnoringCollectionBuilderTest {
+
+  public NullIgnoringCollectionBuilderTest() {}
+
+  @Test
+  public void testNullSafeCollections() {
+    assertThat(
+            NullIgnoringCollectionBuilder.create(new ImmutableList.Builder<Integer>())
+                .getBuilder()
+                .build())
+        .isEqualTo(ImmutableList.of());
+
+    assertThat(
+            NullIgnoringCollectionBuilder.create(new ImmutableList.Builder<Integer>())
+                .add(100)
+                .add(200)
+                .add(null)
+                .getBuilder()
+                .build())
+        .containsExactly(100, 200)
+        .inOrder();
+
+    assertThat(
+            NullIgnoringCollectionBuilder.create(new ImmutableSet.Builder<Integer>())
+                .add(100)
+                .add(200)
+                .add(null)
+                .getBuilder()
+                .build())
+        .containsExactly(100, 200);
+  }
+}