Auto-apply JPA converters for map type (#520)

* Add map converter

* Delete old map usertype

* Refactor bind

* Change to use map entry

* Use Map.Entry

core/src/main/java/google/registry/model/registrar/Registrar.java

@@ -392,8 +392,6 @@ public class Registrar extends ImmutableObject implements Buildable, Jsonifiable
    */
   @Nullable
   @Mapify(CurrencyMapper.class)
-  @org.hibernate.annotations.Type(
-      type = "google.registry.persistence.converter.CurrencyToBillingMapUserType")
   Map<CurrencyUnit, BillingAccountEntry> billingAccountMap;
 
   /** A billing account entry for this registrar, consisting of a currency and an account Id. */

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

@@ -14,6 +14,7 @@
 package google.registry.persistence;
 
 import google.registry.persistence.converter.StringCollectionDescriptor;
+import google.registry.persistence.converter.StringMapDescriptor;
 import java.sql.Types;
 import org.hibernate.boot.model.TypeContributions;
 import org.hibernate.dialect.PostgreSQL95Dialect;
@@ -26,7 +27,7 @@ public class NomulusPostgreSQLDialect extends PostgreSQL95Dialect {
     registerColumnType(Types.VARCHAR, "text");
     registerColumnType(Types.TIMESTAMP_WITH_TIMEZONE, "timestamptz");
     registerColumnType(Types.TIMESTAMP, "timestamptz");
-    registerColumnType(Types.OTHER, "hstore");
+    registerColumnType(StringMapDescriptor.COLUMN_TYPE, StringMapDescriptor.COLUMN_NAME);
     registerColumnType(
         StringCollectionDescriptor.COLUMN_TYPE, StringCollectionDescriptor.COLUMN_DDL_NAME);
   }
@@ -37,5 +38,7 @@ public class NomulusPostgreSQLDialect extends PostgreSQL95Dialect {
     super.contributeTypes(typeContributions, serviceRegistry);
     typeContributions.contributeJavaTypeDescriptor(StringCollectionDescriptor.getInstance());
     typeContributions.contributeSqlTypeDescriptor(StringCollectionDescriptor.getInstance());
+    typeContributions.contributeJavaTypeDescriptor(StringMapDescriptor.getInstance());
+    typeContributions.contributeSqlTypeDescriptor(StringMapDescriptor.getInstance());
   }
 }

core/src/main/java/google/registry/persistence/converter/CurrencyToBillingConverter.java

@@ -0,0 +1,43 @@
+// Copyright 2020 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.persistence.converter;
+
+import static google.registry.model.registrar.Registrar.BillingAccountEntry;
+
+import com.google.common.collect.Maps;
+import java.util.Map;
+import javax.persistence.Converter;
+import org.joda.money.CurrencyUnit;
+
+/** JPA converter for storing/retrieving {@link Map <CurrencyUnit, BillingAccountEntry>} objects. */
+@Converter(autoApply = true)
+public class CurrencyToBillingConverter
+    extends StringMapConverterBase<CurrencyUnit, BillingAccountEntry> {
+
+  @Override
+  Map.Entry<String, String> convertToDatabaseMapEntry(
+      Map.Entry<CurrencyUnit, BillingAccountEntry> entry) {
+    return Maps.immutableEntry(entry.getKey().getCode(), entry.getValue().getAccountId());
+  }
+
+  @Override
+  Map.Entry<CurrencyUnit, BillingAccountEntry> convertToEntityMapEntry(
+      Map.Entry<String, String> entry) {
+    CurrencyUnit currencyUnit = CurrencyUnit.of(entry.getKey());
+    BillingAccountEntry billingAccountEntry =
+        new BillingAccountEntry(currencyUnit, entry.getValue());
+    return Maps.immutableEntry(currencyUnit, billingAccountEntry);
+  }
+}

core/src/main/java/google/registry/persistence/converter/CurrencyToBillingMapUserType.java

@@ -1,54 +0,0 @@
-// Copyright 2020 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.persistence.converter;
-
-import static com.google.common.collect.ImmutableMap.toImmutableMap;
-
-import google.registry.model.registrar.Registrar.BillingAccountEntry;
-import java.util.Map;
-import org.hibernate.usertype.UserType;
-import org.joda.money.CurrencyUnit;
-
-/**
- * A custom {@link UserType} for storing/retrieving {@link Map<CurrencyUnit, BillingAccountEntry>}
- * objects.
- */
-public class CurrencyToBillingMapUserType extends MapUserType {
-
-  @Override
-  public Object toEntityTypeMap(Map<String, String> map) {
-    return map == null
-        ? null
-        : map.entrySet().stream()
-            .collect(
-                toImmutableMap(
-                    entry -> CurrencyUnit.of(entry.getKey()),
-                    entry ->
-                        new BillingAccountEntry(
-                            CurrencyUnit.of(entry.getKey()), entry.getValue())));
-  }
-
-  @Override
-  public Map<String, String> toDbSupportedMap(Object map) {
-    return map == null
-        ? null
-        : ((Map<CurrencyUnit, BillingAccountEntry>) map)
-            .entrySet().stream()
-                .collect(
-                    toImmutableMap(
-                        entry -> entry.getKey().getCode(),
-                        entry -> entry.getValue().getAccountId()));
-  }
-}

core/src/main/java/google/registry/persistence/converter/MapUserType.java

@@ -1,73 +0,0 @@
-// Copyright 2020 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.persistence.converter;
-
-import java.sql.PreparedStatement;
-import java.sql.ResultSet;
-import java.sql.SQLException;
-import java.sql.Types;
-import java.util.Map;
-import org.hibernate.HibernateException;
-import org.hibernate.engine.spi.SharedSessionContractImplementor;
-import org.hibernate.usertype.UserType;
-
-/**
- * A custom {@link UserType} used to convert a Java {@link Map<String, String>} to/from PostgreSQL
- * hstore type. Per this <a href="https://www.postgresql.org/docs/current/hstore.html">doc</a>, as
- * hstore keys and values are simply text strings, the type of key and value in the Java map has to
- * be {@link String} as well.
- */
-public class MapUserType extends MutableUserType {
-
-  @Override
-  public int[] sqlTypes() {
-    return new int[] {Types.OTHER};
-  }
-
-  @Override
-  public Class returnedClass() {
-    return Map.class;
-  }
-
-  @Override
-  public Object nullSafeGet(
-      ResultSet rs, String[] names, SharedSessionContractImplementor session, Object owner)
-      throws HibernateException, SQLException {
-    return toEntityTypeMap((Map<String, String>) rs.getObject(names[0]));
-  }
-
-  @Override
-  public void nullSafeSet(
-      PreparedStatement st, Object value, int index, SharedSessionContractImplementor session)
-      throws HibernateException, SQLException {
-    st.setObject(index, toDbSupportedMap(value));
-  }
-
-  /**
-   * Subclass can override this method to convert the {@link Map<String, String>} to a {@link Map}
-   * of specific type defined in the entity class.
-   */
-  public Object toEntityTypeMap(Map<String, String> map) {
-    return map;
-  }
-
-  /**
-   * Subclass can override this method to convert the {@link Map} of specific type to a {@link
-   * Map<String, String>} that can be stored in the hstore type column.
-   */
-  public Map<String, String> toDbSupportedMap(Object map) {
-    return (Map<String, String>) map;
-  }
-}

core/src/main/java/google/registry/persistence/converter/MutableUserType.java

@@ -1,63 +0,0 @@
-// Copyright 2020 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.persistence.converter;
-
-import java.io.Serializable;
-import java.util.Objects;
-import org.hibernate.HibernateException;
-import org.hibernate.usertype.UserType;
-
-/**
- * An abstract class represents a mutable Hibernate user type which implements related methods
- * defined in {@link UserType}.
- */
-public abstract class MutableUserType implements UserType {
-
-  @Override
-  public boolean equals(Object x, Object y) throws HibernateException {
-    return Objects.equals(x, y);
-  }
-
-  @Override
-  public int hashCode(Object x) throws HibernateException {
-    return x == null ? 0 : x.hashCode();
-  }
-
-  // TODO(b/147489651): Investigate how to properly implement the below methods.
-  @Override
-  public Object deepCopy(Object value) throws HibernateException {
-    return value;
-  }
-
-  @Override
-  public boolean isMutable() {
-    return false;
-  }
-
-  @Override
-  public Serializable disassemble(Object value) throws HibernateException {
-    return (Serializable) value;
-  }
-
-  @Override
-  public Object assemble(Serializable cached, Object owner) throws HibernateException {
-    return cached;
-  }
-
-  @Override
-  public Object replace(Object original, Object target, Object owner) throws HibernateException {
-    return original;
-  }
-}

core/src/main/java/google/registry/persistence/converter/StringMapConverterBase.java

@@ -0,0 +1,52 @@
+// Copyright 2020 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.persistence.converter;
+
+import static com.google.common.collect.ImmutableMap.toImmutableMap;
+
+import google.registry.persistence.converter.StringMapDescriptor.StringMap;
+import java.util.Map;
+import javax.persistence.AttributeConverter;
+
+/**
+ * Base JPA converter for {@link Map} objects that are stored in a column with data type of hstore
+ * in the database.
+ */
+public abstract class StringMapConverterBase<K, V>
+    implements AttributeConverter<Map<K, V>, StringMap> {
+
+  abstract Map.Entry<String, String> convertToDatabaseMapEntry(Map.Entry<K, V> entry);
+
+  abstract Map.Entry<K, V> convertToEntityMapEntry(Map.Entry<String, String> entry);
+
+  @Override
+  public StringMap convertToDatabaseColumn(Map<K, V> attribute) {
+    return attribute == null
+        ? null
+        : StringMap.create(
+            attribute.entrySet().stream()
+                .map(this::convertToDatabaseMapEntry)
+                .collect(toImmutableMap(Map.Entry::getKey, Map.Entry::getValue)));
+  }
+
+  @Override
+  public Map<K, V> convertToEntityAttribute(StringMap dbData) {
+    return dbData == null
+        ? null
+        : dbData.getMap().entrySet().stream()
+            .map(this::convertToEntityMapEntry)
+            .collect(toImmutableMap(Map.Entry::getKey, Map.Entry::getValue));
+  }
+}

core/src/main/java/google/registry/persistence/converter/StringMapDescriptor.java

@@ -0,0 +1,177 @@
+// Copyright 2020 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.persistence.converter;
+
+import static google.registry.persistence.converter.StringMapDescriptor.StringMap;
+
+import com.google.common.collect.ImmutableMap;
+import java.sql.CallableStatement;
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Types;
+import java.util.Map;
+import org.hibernate.type.descriptor.ValueBinder;
+import org.hibernate.type.descriptor.ValueExtractor;
+import org.hibernate.type.descriptor.WrapperOptions;
+import org.hibernate.type.descriptor.java.AbstractTypeDescriptor;
+import org.hibernate.type.descriptor.java.JavaTypeDescriptor;
+import org.hibernate.type.descriptor.spi.JdbcRecommendedSqlTypeMappingContext;
+import org.hibernate.type.descriptor.sql.BasicBinder;
+import org.hibernate.type.descriptor.sql.BasicExtractor;
+import org.hibernate.type.descriptor.sql.SqlTypeDescriptor;
+
+/**
+ * The {@link JavaTypeDescriptor} and {@link SqlTypeDescriptor} for {@link StringMap}.
+ *
+ * <p>A {@link StringMap} object is a simple wrapper for a {@link Map <String, String>} which can be
+ * stored in a column with data type of hstore in the database. The {@link JavaTypeDescriptor} and
+ * {@link SqlTypeDescriptor} is used by JPA/Hibernate to map between the map and hstore which is the
+ * actual type that JDBC uses to read from and write to the database.
+ *
+ * @see <a
+ *     href="https://docs.jboss.org/hibernate/orm/current/userguide/html_single/Hibernate_User_Guide.html#basic-jpa-convert">JPA
+ *     2.1 AttributeConverters</a>
+ * @see <a href="https://www.postgresql.org/docs/current/hstore.html">hstore</a>
+ */
+public class StringMapDescriptor extends AbstractTypeDescriptor<StringMap>
+    implements SqlTypeDescriptor {
+  public static final int COLUMN_TYPE = Types.OTHER;
+  public static final String COLUMN_NAME = "hstore";
+  private static final StringMapDescriptor INSTANCE = new StringMapDescriptor();
+
+  protected StringMapDescriptor() {
+    super(StringMap.class);
+  }
+
+  public static StringMapDescriptor getInstance() {
+    return INSTANCE;
+  }
+
+  @Override
+  public StringMap fromString(String string) {
+    throw new UnsupportedOperationException(
+        "Constructing StringMapDescriptor from string is not allowed");
+  }
+
+  @Override
+  public <X> X unwrap(StringMap value, Class<X> type, WrapperOptions options) {
+    if (value == null) {
+      return null;
+    }
+    if (Map.class.isAssignableFrom(type)) {
+      return (X) value.getMap();
+    }
+    throw unknownUnwrap(type);
+  }
+
+  @Override
+  public <X> StringMap wrap(X value, WrapperOptions options) {
+    if (value == null) {
+      return null;
+    }
+    if (value instanceof Map) {
+      return StringMap.create((Map<String, String>) value);
+    }
+    throw unknownWrap(value.getClass());
+  }
+
+  @Override
+  public SqlTypeDescriptor getJdbcRecommendedSqlType(JdbcRecommendedSqlTypeMappingContext context) {
+    return this;
+  }
+
+  @Override
+  public int getSqlType() {
+    return COLUMN_TYPE;
+  }
+
+  @Override
+  public boolean canBeRemapped() {
+    return false;
+  }
+
+  @Override
+  public <X> ValueBinder<X> getBinder(JavaTypeDescriptor<X> javaTypeDescriptor) {
+    return new BasicBinder<X>(javaTypeDescriptor, this) {
+      @Override
+      protected void doBind(PreparedStatement st, X value, int index, WrapperOptions options)
+          throws SQLException {
+        st.setObject(index, getStringMap(value));
+      }
+
+      @Override
+      protected void doBind(CallableStatement st, X value, String name, WrapperOptions options)
+          throws SQLException {
+        st.setObject(name, getStringMap(value));
+      }
+
+      private Map<String, String> getStringMap(X value) {
+        if (value == null) {
+          return null;
+        }
+        if (value instanceof StringMap) {
+          return ((StringMap) value).getMap();
+        } else {
+          throw new UnsupportedOperationException(
+              String.format(
+                  "Binding type %s is not supported by StringMapDescriptor",
+                  value.getClass().getName()));
+        }
+      }
+    };
+  }
+
+  @Override
+  public <X> ValueExtractor<X> getExtractor(JavaTypeDescriptor<X> javaTypeDescriptor) {
+    return new BasicExtractor<X>(javaTypeDescriptor, this) {
+      @Override
+      protected X doExtract(ResultSet rs, String name, WrapperOptions options) throws SQLException {
+        return javaTypeDescriptor.wrap(rs.getObject(name), options);
+      }
+
+      @Override
+      protected X doExtract(CallableStatement statement, int index, WrapperOptions options)
+          throws SQLException {
+        return javaTypeDescriptor.wrap(statement.getObject(index), options);
+      }
+
+      @Override
+      protected X doExtract(CallableStatement statement, String name, WrapperOptions options)
+          throws SQLException {
+        return javaTypeDescriptor.wrap(statement.getObject(name), options);
+      }
+    };
+  }
+
+  /** A simple wrapper class for {@link Map<String, String>}. */
+  public static class StringMap {
+    private Map<String, String> map;
+
+    private StringMap(Map<String, String> map) {
+      this.map = map;
+    }
+
+    /** Constructs an instance of {@link StringMap} from the given map. */
+    public static StringMap create(Map<String, String> map) {
+      return new StringMap(ImmutableMap.copyOf(map));
+    }
+
+    /** Returns the underlying {@link Map<String, String>} object. */
+    public Map<String, String> getMap() {
+      return map;
+    }
+  }
+}

core/src/main/resources/META-INF/persistence.xml

@@ -36,6 +36,7 @@
     <class>google.registry.persistence.converter.BloomFilterConverter</class>
     <class>google.registry.persistence.converter.CidrAddressBlockListConverter</class>
     <class>google.registry.persistence.converter.CreateAutoTimestampConverter</class>
+    <class>google.registry.persistence.converter.CurrencyToBillingConverter</class>
     <class>google.registry.persistence.converter.CurrencyUnitConverter</class>
     <class>google.registry.persistence.converter.DateTimeConverter</class>
     <class>google.registry.persistence.converter.DurationConverter</class>

core/src/test/java/google/registry/persistence/converter/CidrAddressBlockListConverterTest.java

@@ -32,7 +32,7 @@ import org.junit.runners.JUnit4;
 
 /** Unit tests for {@link CidrAddressBlockListConverter}. */
 @RunWith(JUnit4.class)
-public class CidrAddressBlockListUserTypeTest {
+public class CidrAddressBlockListConverterTest {
   @Rule
   public final JpaUnitTestRule jpaRule =
       new JpaTestRules.Builder().withEntityClass(TestEntity.class).buildUnitTestRule();

core/src/test/java/google/registry/persistence/converter/CurrencyToBillingConverterTest.java

@@ -25,16 +25,15 @@ import google.registry.persistence.transaction.JpaTestRules.JpaUnitTestRule;
 import java.util.Map;
 import javax.persistence.Entity;
 import javax.persistence.Id;
-import org.hibernate.annotations.Type;
 import org.joda.money.CurrencyUnit;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
 
-/** Unit tests for {@link CurrencyToBillingMapUserType}. */
+/** Unit tests for {@link CurrencyToBillingConverter}. */
 @RunWith(JUnit4.class)
-public class CurrencyToBillingMapUserTypeTest {
+public class CurrencyToBillingConverterTest {
   @Rule
   public final JpaUnitTestRule jpaRule =
       new JpaTestRules.Builder()
@@ -62,7 +61,6 @@ public class CurrencyToBillingMapUserTypeTest {
 
     @Id String name = "id";
 
-    @Type(type = "google.registry.persistence.converter.CurrencyToBillingMapUserType")
     Map<CurrencyUnit, BillingAccountEntry> currencyToBilling;
 
     private TestEntity() {}

core/src/test/java/google/registry/persistence/converter/StringMapConverterBaseTest.java

@@ -19,54 +19,56 @@ import static google.registry.persistence.transaction.TransactionManagerFactory.
 import static org.junit.Assert.assertThrows;
 
 import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.Maps;
 import google.registry.model.ImmutableObject;
 import google.registry.persistence.transaction.JpaTestRules;
-import google.registry.persistence.transaction.JpaTestRules.JpaUnitTestRule;
 import java.util.Map;
+import javax.persistence.Converter;
 import javax.persistence.Entity;
 import javax.persistence.Id;
 import javax.persistence.NoResultException;
-import org.hibernate.annotations.Type;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
 
-/** Unit tests for {@link MapUserType}. */
+/** Unit tests for {@link StringMapConverterBase}. */
 @RunWith(JUnit4.class)
-public class MapUserTypeTest {
-
-  // Reusing production script sql/flyway/V14__load_extension_for_hstore.sql, which loads the
-  // hstore extension but nothing else.
+public class StringMapConverterBaseTest {
   @Rule
-  public final JpaUnitTestRule jpaRule =
+  public final JpaTestRules.JpaUnitTestRule jpaRule =
       new JpaTestRules.Builder()
           .withInitScript("sql/flyway/V14__load_extension_for_hstore.sql")
-          .withEntityClass(TestEntity.class)
+          .withEntityClass(TestStringMapConverter.class, TestEntity.class)
           .buildUnitTestRule();
 
+  private static final ImmutableMap<Key, Value> MAP =
+      ImmutableMap.of(
+          new Key("key1"), new Value("value1"),
+          new Key("key2"), new Value("value2"),
+          new Key("key3"), new Value("value3"));
+
   @Test
   public void roundTripConversion_returnsSameMap() {
-    Map<String, String> map = ImmutableMap.of("key1", "value1", "key2", "value2");
-    TestEntity testEntity = new TestEntity(map);
+    TestEntity testEntity = new TestEntity(MAP);
     jpaTm().transact(() -> jpaTm().getEntityManager().persist(testEntity));
     TestEntity persisted =
         jpaTm().transact(() -> jpaTm().getEntityManager().find(TestEntity.class, "id"));
-    assertThat(persisted.map).containsExactly("key1", "value1", "key2", "value2");
+    assertThat(persisted.map).containsExactlyEntriesIn(MAP);
   }
 
   @Test
-  public void testMerge_succeeds() {
-    Map<String, String> map = ImmutableMap.of("key1", "value1", "key2", "value2");
-    TestEntity testEntity = new TestEntity(map);
+  public void testUpdateColumn_succeeds() {
+    TestEntity testEntity = new TestEntity(MAP);
     jpaTm().transact(() -> jpaTm().getEntityManager().persist(testEntity));
     TestEntity persisted =
         jpaTm().transact(() -> jpaTm().getEntityManager().find(TestEntity.class, "id"));
-    persisted.map = ImmutableMap.of("key3", "value3");
+    assertThat(persisted.map).containsExactlyEntriesIn(MAP);
+    persisted.map = ImmutableMap.of(new Key("key4"), new Value("value4"));
     jpaTm().transact(() -> jpaTm().getEntityManager().merge(persisted));
     TestEntity updated =
         jpaTm().transact(() -> jpaTm().getEntityManager().find(TestEntity.class, "id"));
-    assertThat(updated.map).containsExactly("key3", "value3");
+    assertThat(updated.map).containsExactly(new Key("key4"), new Value("value4"));
   }
 
   @Test
@@ -79,7 +81,7 @@ public class MapUserTypeTest {
   }
 
   @Test
-  public void testEmptyCollection_writesAndReadsEmptyCollectionSuccessfully() {
+  public void testEmptyMap_writesAndReadsEmptyCollectionSuccessfully() {
     TestEntity testEntity = new TestEntity(ImmutableMap.of());
     jpaTm().transact(() -> jpaTm().getEntityManager().persist(testEntity));
     TestEntity persisted =
@@ -88,7 +90,7 @@ public class MapUserTypeTest {
   }
 
   @Test
-  public void testNativeQuery_succeeds() throws Exception {
+  public void testNativeQuery_succeeds() {
     executeNativeQuery(
         "INSERT INTO \"TestEntity\" (name, map) VALUES ('id', 'key1=>value1, key2=>value2')");
 
@@ -126,17 +128,46 @@ public class MapUserTypeTest {
         .transact(() -> jpaTm().getEntityManager().createNativeQuery(sql).executeUpdate());
   }
 
+  private static class Key extends ImmutableObject {
+    private String key;
+
+    private Key(String key) {
+      this.key = key;
+    }
+  }
+
+  private static class Value extends ImmutableObject {
+    private String value;
+
+    private Value(String value) {
+      this.value = value;
+    }
+  }
+
+  @Converter(autoApply = true)
+  private static class TestStringMapConverter extends StringMapConverterBase<Key, Value> {
+
+    @Override
+    Map.Entry<String, String> convertToDatabaseMapEntry(Map.Entry<Key, Value> entry) {
+      return Maps.immutableEntry(entry.getKey().key, entry.getValue().value);
+    }
+
+    @Override
+    Map.Entry<Key, Value> convertToEntityMapEntry(Map.Entry<String, String> entry) {
+      return Maps.immutableEntry(new Key(entry.getKey()), new Value(entry.getValue()));
+    }
+  }
+
   @Entity(name = "TestEntity") // Override entity name to avoid the nested class reference.
   private static class TestEntity extends ImmutableObject {
 
     @Id String name = "id";
 
-    @Type(type = "google.registry.persistence.converter.MapUserType")
-    Map<String, String> map;
+    Map<Key, Value> map;
 
     private TestEntity() {}
 
-    private TestEntity(Map<String, String> map) {
+    private TestEntity(Map<Key, Value> map) {
       this.map = map;
     }
   }