Convert DatastoreEntity/SqlEntity to return Optional, not List (#894)

* Convert DatastoreEntity/SqlEntity to return Optional, not List

We don't have any entities that convert to more than one entity, so we
can use an Optional instead for clarity and simplicity.

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

@@ -14,7 +14,6 @@
 
 package google.registry.model.contact;
 
-import com.google.common.collect.ImmutableList;
 import com.googlecode.objectify.Key;
 import com.googlecode.objectify.annotation.EntitySubclass;
 import google.registry.model.ImmutableObject;
@@ -111,8 +110,8 @@ public class ContactHistory extends HistoryEntry implements SqlEntity {
 
   // In Datastore, save as a HistoryEntry object regardless of this object's type
   @Override
-  public ImmutableList<DatastoreEntity> toDatastoreEntities() {
+  public Optional<DatastoreEntity> toDatastoreEntity() {
-    return ImmutableList.of(asHistoryEntry());
+    return Optional.of(asHistoryEntry());
   }
 
   /** Class to represent the composite primary key of {@link ContactHistory} entity. */

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

@@ -17,7 +17,6 @@ package google.registry.model.domain;
 import static com.google.common.collect.ImmutableSet.toImmutableSet;
 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.EntitySubclass;
@@ -250,8 +249,8 @@ public class DomainHistory extends HistoryEntry implements SqlEntity {
 
   // In Datastore, save as a HistoryEntry object regardless of this object's type
   @Override
-  public ImmutableList<DatastoreEntity> toDatastoreEntities() {
+  public Optional<DatastoreEntity> toDatastoreEntity() {
-    return ImmutableList.of(asHistoryEntry());
+    return Optional.of(asHistoryEntry());
   }
 
   /** Class to represent the composite primary key of {@link DomainHistory} entity. */

core/src/main/java/google/registry/model/domain/secdns/DomainDsDataHistory.java

@@ -14,11 +14,11 @@
 
 package google.registry.model.domain.secdns;
 
-import com.google.common.collect.ImmutableList;
 import google.registry.model.domain.DomainHistory;
 import google.registry.model.ofy.ObjectifyService;
 import google.registry.schema.replay.DatastoreEntity;
 import google.registry.schema.replay.SqlEntity;
+import java.util.Optional;
 import javax.persistence.Access;
 import javax.persistence.AccessType;
 import javax.persistence.Column;
@@ -86,7 +86,7 @@ public class DomainDsDataHistory extends DomainDsDataBase implements SqlEntity {
   }
 
   @Override
-  public ImmutableList<DatastoreEntity> toDatastoreEntities() {
+  public Optional<DatastoreEntity> toDatastoreEntity() {
-    return ImmutableList.of(); // not persisted in Datastore
+    return Optional.empty(); // Not persisted in Datastore
   }
 }

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

@@ -14,7 +14,6 @@
 
 package google.registry.model.host;
 
-import com.google.common.collect.ImmutableList;
 import com.googlecode.objectify.Key;
 import com.googlecode.objectify.annotation.EntitySubclass;
 import google.registry.model.ImmutableObject;
@@ -112,8 +111,8 @@ public class HostHistory extends HistoryEntry implements SqlEntity {
 
   // In Datastore, save as a HistoryEntry object regardless of this object's type
   @Override
-  public ImmutableList<DatastoreEntity> toDatastoreEntities() {
+  public Optional<DatastoreEntity> toDatastoreEntity() {
-    return ImmutableList.of(asHistoryEntry());
+    return Optional.of(asHistoryEntry());
   }
 
   /** Class to represent the composite primary key of {@link HostHistory} entity. */

core/src/main/java/google/registry/model/ofy/TransactionInfo.java

@@ -29,7 +29,6 @@ import com.google.common.collect.ImmutableSet;
 import com.googlecode.objectify.Key;
 import google.registry.persistence.VKey;
 import google.registry.schema.replay.DatastoreEntity;
-import google.registry.schema.replay.SqlEntity;
 import java.util.Map;
 import org.joda.time.DateTime;
 
@@ -137,10 +136,9 @@ class TransactionInfo {
                         if (entry.getValue().equals(Delete.SENTINEL)) {
                           jpaTm().delete(VKey.from(entry.getKey()));
                         } else {
-                          for (SqlEntity entity :
+                          ((DatastoreEntity) entry.getValue())
-                              ((DatastoreEntity) entry.getValue()).toSqlEntities()) {
+                              .toSqlEntity()
-                            jpaTm().put(entity);
+                              .ifPresent(jpaTm()::put);
-                          }
                         }
                       });
             });

core/src/main/java/google/registry/model/reporting/HistoryEntry.java

@@ -18,7 +18,6 @@ import static com.googlecode.objectify.Key.getKind;
 import static google.registry.util.CollectionUtils.nullToEmptyImmutableCopy;
 
 import com.google.common.annotations.VisibleForTesting;
-import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.googlecode.objectify.Key;
 import com.googlecode.objectify.annotation.Entity;
@@ -45,6 +44,7 @@ import google.registry.model.host.HostResource;
 import google.registry.persistence.VKey;
 import google.registry.schema.replay.DatastoreEntity;
 import google.registry.schema.replay.SqlEntity;
+import java.util.Optional;
 import java.util.Set;
 import javax.annotation.Nullable;
 import javax.persistence.Access;
@@ -314,8 +314,8 @@ public class HistoryEntry extends ImmutableObject implements Buildable, Datastor
 
   // In SQL, save the child type
   @Override
-  public ImmutableList<SqlEntity> toSqlEntities() {
+  public Optional<SqlEntity> toSqlEntity() {
-    return ImmutableList.of((SqlEntity) toChildHistoryEntity());
+    return Optional.of((SqlEntity) toChildHistoryEntity());
   }
 
   /** Creates a {@link VKey} instance from a {@link Key} instance. */

core/src/main/java/google/registry/model/reporting/Spec11ThreatMatch.java

@@ -18,13 +18,13 @@ import static com.google.common.base.Preconditions.checkArgument;
 import static google.registry.util.CollectionUtils.isNullOrEmpty;
 import static google.registry.util.PreconditionsUtils.checkArgumentNotNull;
 
-import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import google.registry.model.Buildable;
 import google.registry.model.ImmutableObject;
 import google.registry.schema.replay.DatastoreEntity;
 import google.registry.schema.replay.SqlEntity;
 import google.registry.util.DomainNameUtils;
+import java.util.Optional;
 import java.util.Set;
 import javax.persistence.Column;
 import javax.persistence.Entity;
@@ -111,8 +111,8 @@ public class Spec11ThreatMatch extends ImmutableObject implements Buildable, Sql
   }
 
   @Override
-  public ImmutableList<DatastoreEntity> toDatastoreEntities() {
+  public Optional<DatastoreEntity> toDatastoreEntity() {
-    return ImmutableList.of(); // not stored in Datastore
+    return Optional.empty(); // Not persisted in Datastore
   }
 
   @Override

core/src/main/java/google/registry/model/tmch/TmchCrl.java

@@ -20,7 +20,6 @@ import static google.registry.persistence.transaction.TransactionManagerFactory.
 import static google.registry.persistence.transaction.TransactionManagerFactory.ofyTm;
 import static google.registry.persistence.transaction.TransactionManagerFactory.tm;
 
-import com.google.common.collect.ImmutableList;
 import com.googlecode.objectify.Key;
 import com.googlecode.objectify.annotation.Entity;
 import google.registry.model.annotations.NotBackedUp;
@@ -28,9 +27,7 @@ import google.registry.model.annotations.NotBackedUp.Reason;
 import google.registry.model.common.CrossTldSingleton;
 import google.registry.model.tmch.TmchCrl.TmchCrlId;
 import google.registry.persistence.VKey;
-import google.registry.schema.replay.DatastoreEntity;
 import google.registry.schema.replay.NonReplicatedEntity;
-import google.registry.schema.replay.SqlEntity;
 import java.io.Serializable;
 import java.util.Optional;
 import javax.annotation.concurrent.Immutable;
@@ -106,16 +103,6 @@ public final class TmchCrl extends CrossTldSingleton implements NonReplicatedEnt
     return updated;
   }
 
-  @Override
-  public ImmutableList<SqlEntity> toSqlEntities() {
-    return ImmutableList.of(); // dually-written
-  }
-
-  @Override
-  public ImmutableList<DatastoreEntity> toDatastoreEntities() {
-    return ImmutableList.of(); // dually-written
-  }
-
   static class TmchCrlId implements Serializable {
 
     @Column(name = "certificateRevocations")

core/src/main/java/google/registry/persistence/transaction/TransactionEntity.java

@@ -14,9 +14,9 @@
 
 package google.registry.persistence.transaction;
 
-import com.google.common.collect.ImmutableList;
 import google.registry.schema.replay.DatastoreEntity;
 import google.registry.schema.replay.SqlEntity;
+import java.util.Optional;
 import javax.persistence.Entity;
 import javax.persistence.GeneratedValue;
 import javax.persistence.GenerationType;
@@ -45,7 +45,7 @@ public class TransactionEntity implements SqlEntity {
   }
 
   @Override
-  public ImmutableList<DatastoreEntity> toDatastoreEntities() {
+  public Optional<DatastoreEntity> toDatastoreEntity() {
-    return ImmutableList.of(); // not stored in Datastore per se
+    return Optional.empty(); // Not persisted in Datastore per se
   }
 }

core/src/main/java/google/registry/schema/cursor/Cursor.java

@@ -16,7 +16,6 @@ package google.registry.schema.cursor;
 
 import static com.google.appengine.api.search.checkers.Preconditions.checkNotNull;
 
-import com.google.common.collect.ImmutableList;
 import google.registry.model.ImmutableObject;
 import google.registry.model.UpdateAutoTimestamp;
 import google.registry.model.common.Cursor.CursorType;
@@ -26,6 +25,7 @@ import google.registry.schema.replay.SqlEntity;
 import google.registry.util.DateTimeUtils;
 import java.io.Serializable;
 import java.time.ZonedDateTime;
+import java.util.Optional;
 import javax.persistence.Column;
 import javax.persistence.Entity;
 import javax.persistence.EnumType;
@@ -104,8 +104,8 @@ public class Cursor implements SqlEntity {
   }
 
   @Override
-  public ImmutableList<DatastoreEntity> toDatastoreEntities() {
+  public Optional<DatastoreEntity> toDatastoreEntity() {
-    return ImmutableList.of(); // Cursors are not converted since they are ephemeral
+    return Optional.empty(); // Cursors are not converted since they are ephemeral
   }
 
   static class CursorId extends ImmutableObject implements Serializable {

core/src/main/java/google/registry/schema/domain/RegistryLock.java

@@ -19,7 +19,6 @@ import static google.registry.util.DateTimeUtils.isBeforeOrAt;
 import static google.registry.util.DateTimeUtils.toZonedDateTime;
 import static google.registry.util.PreconditionsUtils.checkArgumentNotNull;
 
-import com.google.common.collect.ImmutableList;
 import google.registry.model.Buildable;
 import google.registry.model.CreateAutoTimestamp;
 import google.registry.model.ImmutableObject;
@@ -234,8 +233,8 @@ public final class RegistryLock extends ImmutableObject implements Buildable, Sq
   }
 
   @Override
-  public ImmutableList<DatastoreEntity> toDatastoreEntities() {
+  public Optional<DatastoreEntity> toDatastoreEntity() {
-    return ImmutableList.of(); // not stored in Datastore
+    return Optional.empty(); // Not persisted in Datastore
   }
 
   /** Builder for {@link google.registry.schema.domain.RegistryLock}. */

core/src/main/java/google/registry/schema/replay/DatastoreAndSqlEntity.java

@@ -14,18 +14,18 @@
 
 package google.registry.schema.replay;
 
-import com.google.common.collect.ImmutableList;
+import java.util.Optional;
 
 /** An entity that has the same Java object representation in SQL and Datastore. */
 public interface DatastoreAndSqlEntity extends DatastoreEntity, SqlEntity {
 
   @Override
-  default ImmutableList<DatastoreEntity> toDatastoreEntities() {
+  default Optional<DatastoreEntity> toDatastoreEntity() {
-    return ImmutableList.of(this);
+    return Optional.of(this);
   }
 
   @Override
-  default ImmutableList<SqlEntity> toSqlEntities() {
+  default Optional<SqlEntity> toSqlEntity() {
-    return ImmutableList.of(this);
+    return Optional.of(this);
   }
 }

core/src/main/java/google/registry/schema/replay/DatastoreEntity.java

@@ -14,7 +14,7 @@
 
 package google.registry.schema.replay;
 
-import com.google.common.collect.ImmutableList;
+import java.util.Optional;
 
 /**
  * An object that can be stored in Datastore and serialized using Objectify's {@link
@@ -26,5 +26,5 @@ import com.google.common.collect.ImmutableList;
  */
 public interface DatastoreEntity {
 
-  ImmutableList<SqlEntity> toSqlEntities();
+  Optional<SqlEntity> toSqlEntity();
 }

core/src/main/java/google/registry/schema/replay/DatastoreOnlyEntity.java

@@ -14,11 +14,12 @@
 
 package google.registry.schema.replay;
 
-import com.google.common.collect.ImmutableList;
+import java.util.Optional;
 
+/** An entity that is only stored in Datastore, that should not be replayed to SQL. */
 public interface DatastoreOnlyEntity extends DatastoreEntity {
   @Override
-  default ImmutableList<SqlEntity> toSqlEntities() {
+  default Optional<SqlEntity> toSqlEntity() {
-    return ImmutableList.of();
+    return Optional.empty();
   }
 }

core/src/main/java/google/registry/schema/replay/NonReplicatedEntity.java

@@ -14,7 +14,7 @@
 
 package google.registry.schema.replay;
 
-import com.google.common.collect.ImmutableList;
+import java.util.Optional;
 
 /**
  * Represents an entity that should not participate in asynchronous replication.
@@ -24,12 +24,12 @@ import com.google.common.collect.ImmutableList;
 public interface NonReplicatedEntity extends DatastoreEntity, SqlEntity {
 
   @Override
-  default ImmutableList<DatastoreEntity> toDatastoreEntities() {
+  default Optional<DatastoreEntity> toDatastoreEntity() {
-    return ImmutableList.of();
+    return Optional.empty();
   }
 
   @Override
-  default ImmutableList<SqlEntity> toSqlEntities() {
+  default Optional<SqlEntity> toSqlEntity() {
-    return ImmutableList.of();
+    return Optional.empty();
   }
 }

core/src/main/java/google/registry/schema/replay/SqlEntity.java

@@ -14,7 +14,7 @@
 
 package google.registry.schema.replay;
 
-import com.google.common.collect.ImmutableList;
+import java.util.Optional;
 
 /**
  * An object that can be stored in Cloud SQL using {@link
@@ -25,5 +25,5 @@ import com.google.common.collect.ImmutableList;
  */
 public interface SqlEntity {
 
-  ImmutableList<DatastoreEntity> toDatastoreEntities();
+  Optional<DatastoreEntity> toDatastoreEntity();
 }

core/src/main/java/google/registry/schema/replay/SqlReplayCheckpoint.java

@@ -18,7 +18,7 @@ import static google.registry.model.common.CrossTldSingleton.SINGLETON_ID;
 import static google.registry.persistence.transaction.TransactionManagerFactory.jpaTm;
 import static google.registry.util.DateTimeUtils.START_OF_TIME;
 
-import com.google.common.collect.ImmutableList;
+import java.util.Optional;
 import javax.persistence.Entity;
 import javax.persistence.Id;
 import org.joda.time.DateTime;
@@ -32,8 +32,8 @@ public class SqlReplayCheckpoint implements SqlEntity {
   private DateTime lastReplayTime;
 
   @Override
-  public ImmutableList<DatastoreEntity> toDatastoreEntities() {
+  public Optional<DatastoreEntity> toDatastoreEntity() {
-    return ImmutableList.of(); // not necessary to persist in Datastore
+    return Optional.empty(); // Not necessary to persist in Datastore
   }
 
   public static DateTime get() {

core/src/main/java/google/registry/schema/server/Lock.java

@@ -16,7 +16,6 @@ package google.registry.schema.server;
 
 import static google.registry.util.PreconditionsUtils.checkArgumentNotNull;
 
-import com.google.common.collect.ImmutableList;
 import google.registry.model.ImmutableObject;
 import google.registry.schema.replay.DatastoreEntity;
 import google.registry.schema.replay.SqlEntity;
@@ -24,6 +23,7 @@ import google.registry.schema.server.Lock.LockId;
 import google.registry.util.DateTimeUtils;
 import java.io.Serializable;
 import java.time.ZonedDateTime;
+import java.util.Optional;
 import javax.persistence.Column;
 import javax.persistence.Entity;
 import javax.persistence.Id;
@@ -120,8 +120,8 @@ public class Lock implements SqlEntity {
   }
 
   @Override
-  public ImmutableList<DatastoreEntity> toDatastoreEntities() {
+  public Optional<DatastoreEntity> toDatastoreEntity() {
-    return ImmutableList.of(); // Locks are not converted since they are ephemeral
+    return Optional.empty(); // Locks are not converted since they are ephemeral
   }
 
   static class LockId extends ImmutableObject implements Serializable {

core/src/main/java/google/registry/schema/tld/PremiumEntry.java

@@ -14,13 +14,13 @@
 
 package google.registry.schema.tld;
 
-import com.google.common.collect.ImmutableList;
 import google.registry.model.ImmutableObject;
 import google.registry.model.registry.label.PremiumList;
 import google.registry.schema.replay.DatastoreEntity;
 import google.registry.schema.replay.SqlEntity;
 import java.io.Serializable;
 import java.math.BigDecimal;
+import java.util.Optional;
 import javax.persistence.Column;
 import javax.persistence.Entity;
 import javax.persistence.Id;
@@ -47,7 +47,7 @@ public class PremiumEntry extends ImmutableObject implements Serializable, SqlEn
   private PremiumEntry() {}
 
   @Override
-  public ImmutableList<DatastoreEntity> toDatastoreEntities() {
+  public Optional<DatastoreEntity> toDatastoreEntity() {
-    return ImmutableList.of(); // PremiumList is dually-written
+    return Optional.empty(); // PremiumList is dually-written
   }
 }