Polishing.

Use Standard Exception handling for JDBC SQLException. Introduce easier and consistent mechanism to construct JdbcCustomConversions. Add tests and fix mocking setup. Fix typos.

See #1828
Original pull request #2062

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/core/convert/JdbcCustomConversions.java

@@ -15,13 +15,23 @@
  */
 package org.springframework.data.jdbc.core.convert;
 
+import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
+import java.util.function.Consumer;
 
+import org.springframework.core.convert.converter.Converter;
+import org.springframework.core.convert.converter.ConverterFactory;
+import org.springframework.core.convert.converter.GenericConverter;
 import org.springframework.core.convert.converter.GenericConverter.ConvertiblePair;
+import org.springframework.data.convert.ConverterBuilder;
 import org.springframework.data.convert.CustomConversions;
 import org.springframework.data.jdbc.core.mapping.JdbcSimpleTypes;
+import org.springframework.data.relational.core.dialect.Dialect;
+import org.springframework.lang.Contract;
+import org.springframework.util.Assert;
 
 /**
  * Value object to capture custom conversion. {@link JdbcCustomConversions} also act as factory for
@@ -50,10 +60,10 @@ public class JdbcCustomConversions extends CustomConversions {
 	 * Create a new {@link JdbcCustomConversions} instance registering the given converters and the default store
 	 * converters.
 	 *
-	 * @param converters must not be {@literal null}.
+	 * @param userConverters must not be {@literal null}.
 	 */
-	public JdbcCustomConversions(List<?> converters) {
-		super(constructConverterConfiguration(converters));
+	public JdbcCustomConversions(List<?> userConverters) {
+		this(StoreConversions.of(JdbcSimpleTypes.HOLDER, STORE_CONVERTERS), userConverters);
 	}
 
 	/**
@@ -63,12 +73,7 @@ public class JdbcCustomConversions extends CustomConversions {
 	 * @since 2.3
 	 */
 	public JdbcCustomConversions(StoreConversions storeConversions, List<?> userConverters) {
-
-		super(new ConverterConfiguration( //
-				storeConversions, //
-				userConverters, //
-				JdbcCustomConversions::excludeConversionsBetweenDateAndJsr310Types //
-		));
+		super(JdbcConverterConfigurer.from(storeConversions).registerConverters(userConverters).createConfiguration());
 	}
 
 	/**
@@ -82,15 +87,40 @@ public class JdbcCustomConversions extends CustomConversions {
 		super(converterConfiguration);
 	}
 
-	private static ConverterConfiguration constructConverterConfiguration(List<?> converters) {
+	/**
+	 * Create a new {@link JdbcCustomConversions} from the given {@link Dialect} and {@code converters}.
+	 *
+	 * @param dialect must not be {@literal null}.
+	 * @param converters must not be {@literal null}.
+	 * @return a new {@link JdbcCustomConversions} instance configured from the given dialect and configured converters.
+	 * @since 4.0
+	 */
+	public static JdbcCustomConversions of(Dialect dialect, Collection<?> converters) {
+
+		Assert.notNull(dialect, "Dialect must not be null");
+		Assert.notNull(converters, "Converters must not be null");
 
-		return new ConverterConfiguration( //
-				StoreConversions.of(JdbcSimpleTypes.HOLDER, STORE_CONVERTERS), //
-				converters, //
-				JdbcCustomConversions::excludeConversionsBetweenDateAndJsr310Types //
-		);
+		return create(dialect, configurer -> configurer.registerConverters(converters));
 	}
 
+	/**
+	 * Create a new {@link JdbcCustomConversions} instance using the given {@link Dialect} and
+	 * {@link JdbcConverterConfigurer} callback to configure converters.
+	 *
+	 * @param dialect the {@link Dialect} to use, must not be {@literal null}.
+	 * @param configurer the configurer callback to configure converters, must not be {@literal null}.
+	 * @return a new {@link JdbcCustomConversions} instance configured from the given dialect and configured converters.
+	 */
+	public static JdbcCustomConversions create(Dialect dialect, Consumer<JdbcConverterConfigurer> configurer) {
+
+		Assert.notNull(dialect, "Dialect must not be null");
+		Assert.notNull(configurer, "JdbcConverterConfigurer Consumer must not be null");
+
+		JdbcConverterConfigurer converterConfigurer = JdbcConverterConfigurer.from(dialect);
+		configurer.accept(converterConfigurer);
+
+		return new JdbcCustomConversions(converterConfigurer.createConfiguration());
+	}
 
 	/**
 	 * Obtain a read only copy of default store converters.
@@ -118,4 +148,112 @@ public class JdbcCustomConversions extends CustomConversions {
 	private static boolean excludeConversionsBetweenDateAndJsr310Types(ConvertiblePair cp) {
 		return !isDateTimeApiConversion(cp);
 	}
+
+	/**
+	 * {@link JdbcConverterConfigurer} encapsulates creation of
+	 * {@link org.springframework.data.convert.CustomConversions.ConverterConfiguration} with JDBC specifics.
+	 *
+	 * @author Mark Paluch
+	 * @since 4.0
+	 */
+	public static class JdbcConverterConfigurer {
+
+		private final StoreConversions storeConversions;
+		private final List<Object> customConverters = new ArrayList<>();
+
+		private JdbcConverterConfigurer(StoreConversions storeConversions) {
+			this.storeConversions = storeConversions;
+		}
+
+		/**
+		 * Create a {@link JdbcConverterConfigurer} using the provided {@code dialect} and our own codecs for JSR-310 types.
+		 *
+		 * @param dialect must not be {@literal null}.
+		 * @return
+		 */
+		static JdbcConverterConfigurer from(Dialect dialect) {
+
+			List<Object> converters = new ArrayList<>();
+			converters.addAll(dialect.getConverters());
+			converters.addAll(JdbcCustomConversions.storeConverters());
+
+			StoreConversions storeConversions = StoreConversions.of(JdbcSimpleTypes.HOLDER, converters);
+
+			return new JdbcConverterConfigurer(storeConversions);
+		}
+
+		/**
+		 * Create a {@link JdbcConverterConfigurer} using the provided {@code storeConversions}.
+		 *
+		 * @param storeConversions must not be {@literal null}.
+		 * @return
+		 */
+		static JdbcConverterConfigurer from(StoreConversions storeConversions) {
+			return new JdbcConverterConfigurer(storeConversions);
+		}
+
+		/**
+		 * Add a custom {@link Converter} implementation.
+		 *
+		 * @param converter must not be {@literal null}.
+		 * @return this.
+		 */
+		@Contract("_ -> this")
+		public JdbcConverterConfigurer registerConverter(Converter<?, ?> converter) {
+
+			Assert.notNull(converter, "Converter must not be null");
+			customConverters.add(converter);
+			return this;
+		}
+
+		/**
+		 * Add {@link Converter converters}, {@link ConverterFactory factories}, {@link ConverterBuilder.ConverterAware
+		 * converter-aware objects}, and {@link GenericConverter generic converters}.
+		 *
+		 * @param converters must not be {@literal null} nor contain {@literal null} values.
+		 * @return this.
+		 */
+		@Contract("_ -> this")
+		public JdbcConverterConfigurer registerConverters(Object... converters) {
+			return registerConverters(Arrays.asList(converters));
+		}
+
+		/**
+		 * Add {@link Converter converters}, {@link ConverterFactory factories}, {@link ConverterBuilder.ConverterAware
+		 * converter-aware objects}, and {@link GenericConverter generic converters}.
+		 *
+		 * @param converters must not be {@literal null} nor contain {@literal null} values.
+		 * @return this.
+		 */
+		@Contract("_ -> this")
+		public JdbcConverterConfigurer registerConverters(Collection<?> converters) {
+
+			Assert.notNull(converters, "Converters must not be null");
+			Assert.noNullElements(converters, "Converters must not be null nor contain null values");
+
+			customConverters.addAll(converters);
+			return this;
+		}
+
+		/**
+		 * Add a custom {@link ConverterFactory} implementation.
+		 *
+		 * @param converterFactory must not be {@literal null}.
+		 * @return this.
+		 */
+		@Contract("_ -> this")
+		public JdbcConverterConfigurer registerConverterFactory(ConverterFactory<?, ?> converterFactory) {
+
+			Assert.notNull(converterFactory, "ConverterFactory must not be null");
+			customConverters.add(converterFactory);
+			return this;
+		}
+
+		ConverterConfiguration createConfiguration() {
+			return new ConverterConfiguration(storeConversions, this.customConverters,
+					JdbcCustomConversions::excludeConversionsBetweenDateAndJsr310Types);
+		}
+
+	}
+
 }

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/core/convert/MappingJdbcConverter.java

@@ -20,15 +20,14 @@ import java.sql.JDBCType;
 import java.sql.SQLException;
 import java.sql.SQLType;
 import java.util.Iterator;
+import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 import java.util.function.Function;
 
-import org.apache.commons.logging.Log;
-import org.apache.commons.logging.LogFactory;
 import org.springframework.context.ApplicationContextAware;
 import org.springframework.core.convert.converter.Converter;
-import org.springframework.dao.NonTransientDataAccessException;
+import org.springframework.dao.DataAccessException;
 import org.springframework.data.convert.CustomConversions;
 import org.springframework.data.jdbc.core.mapping.AggregateReference;
 import org.springframework.data.jdbc.core.mapping.JdbcValue;
@@ -46,6 +45,10 @@ import org.springframework.data.relational.core.mapping.RelationalPersistentEnti
 import org.springframework.data.relational.core.mapping.RelationalPersistentProperty;
 import org.springframework.data.relational.domain.RowDocument;
 import org.springframework.data.util.TypeInformation;
+import org.springframework.jdbc.UncategorizedSQLException;
+import org.springframework.jdbc.support.SQLErrorCodeSQLExceptionTranslator;
+import org.springframework.jdbc.support.SQLExceptionSubclassTranslator;
+import org.springframework.jdbc.support.SQLExceptionTranslator;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
@@ -67,9 +70,9 @@ import org.springframework.util.Assert;
  */
 public class MappingJdbcConverter extends MappingRelationalConverter implements JdbcConverter, ApplicationContextAware {
 
-	private static final Log LOG = LogFactory.getLog(MappingJdbcConverter.class);
 	private static final Converter<Iterable<?>, Map<?, ?>> ITERABLE_OF_ENTRY_TO_MAP_CONVERTER = new IterableOfEntryToMapConverter();
 
+	private SQLExceptionTranslator exceptionTranslator = new SQLExceptionSubclassTranslator();
 	private final JdbcTypeFactory typeFactory;
 	private final RelationResolver relationResolver;
 
@@ -111,6 +114,15 @@ public class MappingJdbcConverter extends MappingRelationalConverter implements
 		this.relationResolver = relationResolver;
 	}
 
+	/**
+	 * Set the exception translator for this instance. Defaults to a {@link SQLErrorCodeSQLExceptionTranslator}.
+	 *
+	 * @see SQLExceptionSubclassTranslator
+	 */
+	public void setExceptionTranslator(SQLExceptionTranslator exceptionTranslator) {
+		this.exceptionTranslator = exceptionTranslator;
+	}
+
 	@Nullable
 	private Class<?> getEntityColumnType(TypeInformation<?> type) {
 
@@ -189,59 +201,44 @@ public class MappingJdbcConverter extends MappingRelationalConverter implements
 			return null;
 		}
 
-		TypeInformation<?> originalTargetType = targetType;
-		value = readJdbcArray(value);
-		targetType = determineNestedTargetType(targetType);
+		value = potentiallyUnwrapArray(value);
 
-		return possiblyReadToAggregateReference(getPotentiallyConvertedSimpleRead(value, targetType), originalTargetType);
+		if (AggregateReference.class.isAssignableFrom(targetType.getType())) {
+
+			List<TypeInformation<?>> types = targetType.getTypeArguments();
+			TypeInformation<?> idType = types.get(1);
+			if (value instanceof AggregateReference<?, ?> ref) {
+				return AggregateReference.to(readValue(ref.getId(), idType));
+			} else {
+				return AggregateReference.to(readValue(value, idType));
+			}
+		}
+
+		return getPotentiallyConvertedSimpleRead(value, targetType);
 	}
 
 	/**
 	 * Unwrap a Jdbc array, if such a value is provided
 	 */
-	private Object readJdbcArray(Object value) {
+	private Object potentiallyUnwrapArray(Object value) {
 
 		if (value instanceof Array array) {
 			try {
 				return array.getArray();
 			} catch (SQLException e) {
-				throw new FailedToAccessJdbcArrayException(e);
+				throw translateException("Array.getArray()", null, e);
 			}
 		}
 
 		return value;
 	}
 
-	/**
-	 * Determine the id type of an {@link AggregateReference} that the rest of the conversion infrastructure needs to use
-	 * as a conversion target.
-	 */
-	private TypeInformation<?> determineNestedTargetType(TypeInformation<?> ultimateTargetType) {
-
-		if (AggregateReference.class.isAssignableFrom(ultimateTargetType.getType())) {
-			// the id type of a AggregateReference
-			return ultimateTargetType.getTypeArguments().get(1);
-		}
-		return ultimateTargetType;
-	}
-
-	/**
-	 * Convert value to an {@link AggregateReference} if that is specified by the parameter targetType.
-	 */
-	private Object possiblyReadToAggregateReference(Object value, TypeInformation<?> targetType) {
-
-		if (AggregateReference.class.isAssignableFrom(targetType.getType())) {
-			return AggregateReference.to(value);
-		}
-		return value;
-	}
-
 	@Nullable
 	@Override
 	protected Object getPotentiallyConvertedSimpleWrite(Object value, TypeInformation<?> type) {
 
-		if (value instanceof AggregateReference<?, ?> aggregateReference) {
-			return writeValue(aggregateReference.getId(), type);
+		if (value instanceof AggregateReference<?, ?> ref) {
+			return writeValue(ref.getId(), type);
 		}
 
 		return super.getPotentiallyConvertedSimpleWrite(value, type);
@@ -277,11 +274,11 @@ public class MappingJdbcConverter extends MappingRelationalConverter implements
 	public JdbcValue writeJdbcValue(@Nullable Object value, TypeInformation<?> columnType, SQLType sqlType) {
 
 		TypeInformation<?> targetType = canWriteAsJdbcValue(value) ? TypeInformation.of(JdbcValue.class) : columnType;
-		
-		if (value instanceof AggregateReference<?, ?> aggregateReference) {
-			return writeJdbcValue(aggregateReference.getId(), columnType, sqlType);
+
+		if (value instanceof AggregateReference<?, ?> ref) {
+			return writeJdbcValue(ref.getId(), columnType, sqlType);
 		}
-		
+
 		Object convertedValue = writeValue(value, targetType);
 
 		if (convertedValue instanceof JdbcValue result) {
@@ -306,7 +303,7 @@ public class MappingJdbcConverter extends MappingRelationalConverter implements
 
 			return JdbcValue.of(convertedValue, JDBCType.BINARY);
 		}
-		
+
 		return JdbcValue.of(convertedValue, sqlType);
 	}
 
@@ -340,10 +337,18 @@ public class MappingJdbcConverter extends MappingRelationalConverter implements
 		return super.newValueProvider(documentAccessor, evaluator, context);
 	}
 
-	private static class FailedToAccessJdbcArrayException extends NonTransientDataAccessException {
-		public FailedToAccessJdbcArrayException(SQLException e) {
-			super("Failed to read array", e);
-		}
+	/**
+	 * Translate the given {@link SQLException} into a generic {@link DataAccessException}.
+	 *
+	 * @param task readable text describing the task being attempted
+	 * @param sql the SQL query or update that caused the problem (can be {@code null})
+	 * @param ex the offending {@code SQLException}
+	 * @return a DataAccessException wrapping the {@code SQLException} (never {@code null})
+	 */
+	private DataAccessException translateException(String task, @org.jspecify.annotations.Nullable String sql,
+			SQLException ex) {
+		DataAccessException dae = exceptionTranslator.translate(task, sql, ex);
+		return (dae != null ? dae : new UncategorizedSQLException(task, sql, ex));
 	}
 
 	/**

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/core/mapping/AggregateReference.java

@@ -16,6 +16,7 @@
 package org.springframework.data.jdbc.core.mapping;
 
 import java.util.Objects;
+import java.util.function.Function;
 
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
@@ -31,6 +32,14 @@ import org.springframework.util.Assert;
  */
 public interface AggregateReference<T, ID> {
 
+	/**
+	 * Creates an {@link AggregateReference} that refers to the target aggregate root with the given id.
+	 *
+	 * @param id aggregate identifier. Can be a simple value or an composite id (complex object).
+	 * @return
+	 * @param <T> target aggregate type.
+	 * @param <ID> target aggregate identifier type.
+	 */
 	static <T, ID> AggregateReference<T, ID> to(ID id) {
 		return new IdOnlyAggregateReference<>(id);
 	}

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/repository/config/AbstractJdbcConfiguration.java

@@ -49,7 +49,9 @@ import org.springframework.data.relational.core.mapping.DefaultNamingStrategy;
 import org.springframework.data.relational.core.mapping.NamingStrategy;
 import org.springframework.data.relational.core.mapping.Table;
 import org.springframework.data.util.TypeScanner;
+import org.springframework.jdbc.core.JdbcTemplate;
 import org.springframework.jdbc.core.namedparam.NamedParameterJdbcOperations;
+import org.springframework.jdbc.core.namedparam.NamedParameterJdbcTemplate;
 import org.springframework.util.StringUtils;
 
 /**
@@ -155,7 +157,15 @@ public class AbstractJdbcConfiguration implements ApplicationContextAware {
 				: JdbcArrayColumns.DefaultSupport.INSTANCE;
 		DefaultJdbcTypeFactory jdbcTypeFactory = new DefaultJdbcTypeFactory(operations.getJdbcOperations(), arrayColumns);
 
-		return new MappingJdbcConverter(mappingContext, relationResolver, conversions, jdbcTypeFactory);
+		MappingJdbcConverter mappingJdbcConverter = new MappingJdbcConverter(mappingContext, relationResolver, conversions,
+				jdbcTypeFactory);
+
+		if (operations instanceof NamedParameterJdbcTemplate namedParameterJdbcTemplate
+				&& namedParameterJdbcTemplate.getJdbcOperations() instanceof JdbcTemplate jdbcTemplate) {
+			mappingJdbcConverter.setExceptionTranslator(jdbcTemplate.getExceptionTranslator());
+		}
+
+		return mappingJdbcConverter;
 	}
 
 	/**

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/repository/query/StringBasedJdbcQuery.java

@@ -242,7 +242,8 @@ public class StringBasedJdbcQuery extends AbstractJdbcQuery {
 			JdbcParameters.JdbcParameter parameter = getQueryMethod().getParameters()
 					.getParameter(bindableParameter.getIndex());
 
-			JdbcValue jdbcValue = writeValue(value, parameter.getTypeInformation(), parameter);
+			JdbcValue jdbcValue = writeValue(value, parameter.getTypeInformation(),
+					parameter);
 			SQLType jdbcType = jdbcValue.getJdbcType();
 
 			if (jdbcType == null) {

spring-data-jdbc/src/test/java/org/springframework/data/jdbc/core/convert/MappingJdbcConverterAggregateReferenceUnitTests.java

@@ -18,24 +18,41 @@ package org.springframework.data.jdbc.core.convert;
 import static org.assertj.core.api.Assertions.*;
 import static org.mockito.Mockito.*;
 
-import org.assertj.core.api.Assertions;
+import java.util.List;
+
 import org.junit.jupiter.api.Test;
+
+import org.springframework.core.ResolvableType;
+import org.springframework.core.convert.converter.Converter;
 import org.springframework.data.annotation.Id;
+import org.springframework.data.convert.ReadingConverter;
+import org.springframework.data.convert.WritingConverter;
+import org.springframework.data.jdbc.core.dialect.JdbcPostgresDialect;
 import org.springframework.data.jdbc.core.mapping.AggregateReference;
 import org.springframework.data.jdbc.core.mapping.JdbcMappingContext;
 import org.springframework.data.relational.core.mapping.RelationalPersistentEntity;
 import org.springframework.data.relational.core.mapping.RelationalPersistentProperty;
+import org.springframework.data.repository.CrudRepository;
 import org.springframework.data.util.TypeInformation;
 
 /**
  * Unit tests for the handling of {@link AggregateReference}s in the {@link MappingJdbcConverter}.
  *
  * @author Jens Schauder
+ * @author Mark Paluch
  */
 class MappingJdbcConverterAggregateReferenceUnitTests {
 
+	JdbcCustomConversions conversions = JdbcCustomConversions.of(JdbcPostgresDialect.INSTANCE,
+			List.of(AggregateIdToLong.INSTANCE, NumberToAggregateId.INSTANCE));
+
 	JdbcMappingContext context = new JdbcMappingContext();
-	JdbcConverter converter = new MappingJdbcConverter(context, mock(RelationResolver.class));
+	JdbcConverter converter = new MappingJdbcConverter(context, mock(RelationResolver.class), conversions,
+			JdbcTypeFactory.unsupported());
+
+	MappingJdbcConverterAggregateReferenceUnitTests() {
+		context.setSimpleTypeHolder(conversions.getSimpleTypeHolder());
+	}
 
 	RelationalPersistentEntity<?> entity = context.getRequiredPersistentEntity(DummyEntity.class);
 
@@ -46,20 +63,41 @@ class MappingJdbcConverterAggregateReferenceUnitTests {
 
 		Object readValue = converter.readValue(23, property.getTypeInformation());
 
-		Assertions.assertThat(readValue).isInstanceOf(AggregateReference.class);
+		assertThat(readValue).isInstanceOf(AggregateReference.class);
 		assertThat(((AggregateReference<DummyEntity, Long>) readValue).getId()).isEqualTo(23L);
 	}
 
 	@Test // DATAJDBC-221
 	void convertsFromAggregateReference() {
 
-		final RelationalPersistentProperty property = entity.getRequiredPersistentProperty("reference");
+		RelationalPersistentProperty property = entity.getRequiredPersistentProperty("reference");
 
 		AggregateReference<Object, Integer> reference = AggregateReference.to(23);
 
 		Object writeValue = converter.writeValue(reference, TypeInformation.of(converter.getColumnType(property)));
 
-		Assertions.assertThat(writeValue).isEqualTo(23L);
+		assertThat(writeValue).isEqualTo(23L);
+	}
+
+	@Test // GH-1828
+	void considersReadConverter() {
+
+		TypeInformation<?> targetType = TypeInformation
+				.of(ResolvableType.forClassWithGenerics(AggregateReference.class, Object.class, AggregateId.class));
+
+		AggregateReference<Object, Integer> reference = AggregateReference.to(23);
+		AggregateReference<Object, AggregateId> converted = (AggregateReference) converter.readValue(reference, targetType);
+
+		assertThat(converted.getId()).isEqualTo(new AggregateId(23L));
+	}
+
+	@Test // GH-1828
+	void considersWriteConverter() {
+
+		AggregateReference<Object, AggregateId> reference = AggregateReference.to(new AggregateId(23L));
+		Object converted = converter.writeValue(reference, TypeInformation.of(Long.class));
+
+		assertThat(converted).isEqualTo(23L);
 	}
 
 	private static class DummyEntity {
@@ -67,4 +105,55 @@ class MappingJdbcConverterAggregateReferenceUnitTests {
 		@Id Long simple;
 		AggregateReference<DummyEntity, Long> reference;
 	}
+
+	static class AggregateOne {
+
+		@Id Long id;
+		String name;
+		AggregateReference<AggregateTwo, Long> two;
+	}
+
+	static class AggregateTwo {
+
+		@Id Long id;
+		String name;
+	}
+
+	interface ReferencingAggregateRepository extends CrudRepository<ReferencingAggregate, Long> {
+
+	}
+
+	record AggregateWithConvertableId(@Id AggregateId id, String name) {
+
+	}
+
+	record AggregateId(Long value) {
+
+	}
+
+	record ReferencingAggregate(@Id Long id, String name,
+			AggregateReference<AggregateWithConvertableId, AggregateId> ref) {
+	}
+
+	@WritingConverter
+	private enum AggregateIdToLong implements Converter<AggregateId, Long> {
+
+		INSTANCE;
+
+		@Override
+		public Long convert(AggregateId source) {
+			return source.value;
+		}
+	}
+
+	@ReadingConverter
+	private enum NumberToAggregateId implements Converter<Number, AggregateId> {
+
+		INSTANCE;
+
+		@Override
+		public AggregateId convert(Number source) {
+			return new AggregateId(source.longValue());
+		}
+	}
 }

spring-data-jdbc/src/test/java/org/springframework/data/jdbc/repository/JdbcRepositoryCrossAggregateHsqlIntegrationTests.java

@@ -18,8 +18,8 @@ package org.springframework.data.jdbc.repository;
 import static java.util.Arrays.*;
 import static org.assertj.core.api.Assertions.*;
 
-import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
+
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.ComponentScan;
@@ -47,9 +47,7 @@ import org.springframework.test.jdbc.JdbcTestUtils;
  *
  * @author Jens Schauder
  * @author Salim Achouche
- * @author Salim Achouche
  */
-
 @IntegrationTest
 @EnabledOnDatabase(DatabaseType.HSQL)
 public class JdbcRepositoryCrossAggregateHsqlIntegrationTests {
@@ -152,7 +150,8 @@ public class JdbcRepositoryCrossAggregateHsqlIntegrationTests {
 	}
 
 	@WritingConverter
-	enum AggregateIdToLong implements Converter<AggregateId, Long> {
+	private enum AggregateIdToLong implements Converter<AggregateId, Long> {
+
 		INSTANCE;
 
 		@Override
@@ -162,7 +161,8 @@ public class JdbcRepositoryCrossAggregateHsqlIntegrationTests {
 	}
 
 	@ReadingConverter
-	enum NumberToAggregateId implements Converter<Number, AggregateId> {
+	private enum NumberToAggregateId implements Converter<Number, AggregateId> {
+
 		INSTANCE;
 
 		@Override
@@ -170,4 +170,5 @@ public class JdbcRepositoryCrossAggregateHsqlIntegrationTests {
 			return new AggregateId(source.longValue());
 		}
 	}
+
 }

spring-data-jdbc/src/test/java/org/springframework/data/jdbc/repository/JdbcRepositoryIntegrationTests.java

@@ -352,7 +352,7 @@ public class JdbcRepositoryIntegrationTests {
 	@ParameterizedTest
 	@NullSource
 	@EnumSource(value = EnumClass.class) // GH-2007
-	void shouldSaveWithCustomSpellExpressions(EnumClass value) {
+	void shouldSaveWithCustomSpelExpressions(EnumClass value) {
 
 		expressionSqlTypePropagationRepository.saveWithSpel(new ExpressionSqlTypePropagation(1L, value));
 

spring-data-jdbc/src/test/java/org/springframework/data/jdbc/repository/query/StringBasedJdbcQueryUnitTests.java

@@ -100,7 +100,7 @@ class StringBasedJdbcQueryUnitTests {
 
 		this.defaultRowMapper = mock(RowMapper.class);
 		this.operations = mock(NamedParameterJdbcOperations.class);
-		this.context = mock(RelationalMappingContext.class, RETURNS_DEEP_STUBS);
+		this.context = new RelationalMappingContext();
 		this.converter = new MappingJdbcConverter(context, mock(RelationResolver.class));
 		this.delegate = ValueExpressionDelegate.create();
 	}

spring-data-r2dbc/src/test/java/org/springframework/data/r2dbc/core/ReactiveDataAccessStrategyTests.java

@@ -15,6 +15,7 @@
  */
 package org.springframework.data.r2dbc.core;
 
+import static org.assertj.core.api.SoftAssertions.*;
 import static org.mockito.Mockito.*;
 import static org.springframework.data.r2dbc.testing.Assertions.*;
 
@@ -38,19 +39,19 @@ import org.springframework.r2dbc.core.binding.BindTarget;
  *
  * @author Mark Paluch
  */
-public class ReactiveDataAccessStrategyTests {
+class ReactiveDataAccessStrategyTests {
 
-	BindTarget bindTarget = mock(BindTarget.class);
+	private BindTarget bindTarget = mock(BindTarget.class);
 
-	ReactiveDataAccessStrategy strategy = new DefaultReactiveDataAccessStrategy(MySqlDialect.INSTANCE,
+	private ReactiveDataAccessStrategy strategy = new DefaultReactiveDataAccessStrategy(MySqlDialect.INSTANCE,
 			Arrays.asList(UuidToStringConverter.INSTANCE, StringToUuidConverter.INSTANCE));
 
 	@Test // gh-305
-	public void shouldConvertParameter() {
+	void shouldConvertParameter() {
 
 		UUID value = UUID.randomUUID();
 
-		SoftAssertions.assertSoftly(softly -> {
+		assertSoftly(softly -> {
 
 			softly.assertThat(strategy.getBindValue(Parameter.from(value))).isEqualTo(Parameter.from(value.toString()));
 			softly.assertThat(strategy.getBindValue(Parameter.from(Condition.New))).isEqualTo(Parameter.from("New"));
@@ -58,14 +59,14 @@ public class ReactiveDataAccessStrategyTests {
 	}
 
 	@Test // gh-305
-	public void shouldConvertEmptyParameter() {
+	void shouldConvertEmptyParameter() {
 
 		assertThat(strategy.getBindValue(Parameter.empty(UUID.class))).isEqualTo(Parameter.empty(String.class));
 		assertThat(strategy.getBindValue(Parameter.empty(Condition.class))).isEqualTo(Parameter.empty(String.class));
 	}
 
 	@Test // gh-305
-	public void shouldConvertCriteria() {
+	void shouldConvertCriteria() {
 
 		UUID value = UUID.randomUUID();
 
@@ -80,7 +81,7 @@ public class ReactiveDataAccessStrategyTests {
 	}
 
 	@Test // gh-305
-	public void shouldConvertAssignment() {
+	void shouldConvertAssignment() {
 
 		UUID value = UUID.randomUUID();
 

spring-data-relational/src/main/java/org/springframework/data/relational/core/conversion/MappingRelationalConverter.java

@@ -44,7 +44,16 @@ import org.springframework.data.mapping.PersistentProperty;
 import org.springframework.data.mapping.PersistentPropertyAccessor;
 import org.springframework.data.mapping.PersistentPropertyPathAccessor;
 import org.springframework.data.mapping.context.MappingContext;
-import org.springframework.data.mapping.model.*;
+import org.springframework.data.mapping.model.CachingValueExpressionEvaluatorFactory;
+import org.springframework.data.mapping.model.ConvertingPropertyAccessor;
+import org.springframework.data.mapping.model.EntityInstantiator;
+import org.springframework.data.mapping.model.ParameterValueProvider;
+import org.springframework.data.mapping.model.PersistentEntityParameterValueProvider;
+import org.springframework.data.mapping.model.PropertyValueProvider;
+import org.springframework.data.mapping.model.SimpleTypeHolder;
+import org.springframework.data.mapping.model.SpELContext;
+import org.springframework.data.mapping.model.ValueExpressionEvaluator;
+import org.springframework.data.mapping.model.ValueExpressionParameterValueProvider;
 import org.springframework.data.projection.EntityProjection;
 import org.springframework.data.projection.EntityProjectionIntrospector;
 import org.springframework.data.projection.EntityProjectionIntrospector.ProjectionPredicate;
@@ -679,7 +688,7 @@ public class MappingRelationalConverter extends AbstractRelationalConverter
 		}
 
 		// custom conversion
-		Optional<Class<?>> customWriteTarget = determinCustomWriteTarget(value, type);
+		Optional<Class<?>> customWriteTarget = determineCustomWriteTarget(value, type);
 
 		if (customWriteTarget.isPresent()) {
 			return getConversionService().convert(value, customWriteTarget.get());
@@ -688,7 +697,7 @@ public class MappingRelationalConverter extends AbstractRelationalConverter
 		return getPotentiallyConvertedSimpleWrite(value, type);
 	}
 
-	private Optional<Class<?>> determinCustomWriteTarget(Object value, TypeInformation<?> type) {
+	private Optional<Class<?>> determineCustomWriteTarget(Object value, TypeInformation<?> type) {
 
 		return getConversions().getCustomWriteTarget(value.getClass(), type.getType())
 				.or(() -> getConversions().getCustomWriteTarget(type.getType()))
@@ -721,10 +730,11 @@ public class MappingRelationalConverter extends AbstractRelationalConverter
 			}
 		}
 
-		if (getConversionService().canConvert(value.getClass(), type.getType())) {
-			return getConversionService().convert(value, type.getType());
+		if (type.getType().isInstance(value) || !getConversionService().canConvert(value.getClass(), type.getType())) {
+			return value;
 		}
-		return value;
+
+		return getConversionService().convert(value, type.getType());
 	}
 
 	private Object writeArray(Object value, TypeInformation<?> type) {