Apply custom conversions for collections.

The target type for the conversion of the complete collection gets adapted when a custom conversion was applied to the elements.

Also `JdbcValue` elements as a result of a custom conversion get unwrapped.

Closes #2078
Original pull request: #2081

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

@@ -255,6 +255,9 @@ public class MappingJdbcConverter extends MappingRelationalConverter implements
 		}
 
 		Class<?> componentType = convertedValue.getClass().getComponentType();
+
+		if (convertedValue.getClass().isArray()) {
+
 		if (componentType != byte.class && componentType != Byte.class) {
 
 			Object[] objectArray = requireObjectArray(convertedValue);
@@ -268,6 +271,24 @@ public class MappingJdbcConverter extends MappingRelationalConverter implements
 		return JdbcValue.of(convertedValue, JDBCType.BINARY);
 	}
 
+		return JdbcValue.of(convertedValue, sqlType);
+	}
+
+	/**
+	 * Unwraps values of type {@link JdbcValue}.
+	 *
+	 * @param convertedValue a value that might need unwrapping.
+	 */
+	@Override
+	@Nullable
+	protected Object unwrap(@Nullable Object convertedValue) {
+
+		if (convertedValue instanceof JdbcValue jdbcValue) {
+			return jdbcValue.getValue();
+		}
+		return convertedValue;
+	}
+
 	@SuppressWarnings("unchecked")
 	@Override
 	public <R> R readAndResolve(TypeInformation<R> type, RowDocument source, Identifier identifier) {

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

@@ -38,8 +38,10 @@ import org.springframework.data.jdbc.core.convert.JdbcCustomConversions;
 import org.springframework.data.jdbc.core.mapping.JdbcValue;
 import org.springframework.data.jdbc.repository.query.Query;
 import org.springframework.data.jdbc.repository.support.JdbcRepositoryFactory;
+import org.springframework.data.jdbc.testing.EnabledOnFeature;
 import org.springframework.data.jdbc.testing.IntegrationTest;
 import org.springframework.data.jdbc.testing.TestConfiguration;
+import org.springframework.data.jdbc.testing.TestDatabaseFeatures;
 import org.springframework.data.repository.CrudRepository;
 
 /**
@@ -61,6 +63,11 @@ public class JdbcRepositoryCustomConversionIntegrationTests {
 			return factory.getRepository(EntityWithStringyBigDecimalRepository.class);
 		}
 
+		@Bean
+		EntityWithDirectionsRepository repositoryWithDirections(JdbcRepositoryFactory factory) {
+			return factory.getRepository(EntityWithDirectionsRepository.class);
+		}
+
 		@Bean
 		JdbcCustomConversions jdbcCustomConversions() {
 			return new JdbcCustomConversions(asList(StringToBigDecimalConverter.INSTANCE, BigDecimalToString.INSTANCE,
@@ -70,6 +77,7 @@ public class JdbcRepositoryCustomConversionIntegrationTests {
 	}
 
 	@Autowired EntityWithStringyBigDecimalRepository repository;
+	@Autowired EntityWithDirectionsRepository repositoryWithDirections;
 
 	/**
 	 * In PostrgreSQL this fails if a simple converter like the following is used.
@@ -162,6 +170,18 @@ public class JdbcRepositoryCustomConversionIntegrationTests {
 				.containsExactly(Direction.CENTER);
 	}
 
+	@Test // GH-2078
+	@EnabledOnFeature(TestDatabaseFeatures.Feature.SUPPORTS_ARRAYS)
+	void saveAndLoadListOfDirectionsAsArray() {
+
+		EntityWithDirections saved = repositoryWithDirections
+				.save(new EntityWithDirections(null, List.of(Direction.CENTER, Direction.RIGHT)));
+
+		EntityWithDirections reloaded = repositoryWithDirections.findById(saved.id).orElseThrow();
+
+		assertThat(reloaded).isEqualTo(saved);
+	}
+
 	interface EntityWithStringyBigDecimalRepository extends CrudRepository<EntityWithStringyBigDecimal, CustomId> {
 
 		@Query("SELECT * FROM ENTITY_WITH_STRINGY_BIG_DECIMAL WHERE DIRECTION IN (:types)")
@@ -171,6 +191,8 @@ public class JdbcRepositoryCustomConversionIntegrationTests {
 		List<EntityWithStringyBigDecimal> findByEnumType(Direction type);
 	}
 
+	interface EntityWithDirectionsRepository extends CrudRepository<EntityWithDirections, Long> {}
+
 	private static class EntityWithStringyBigDecimal {
 
 		@Id CustomId id;
@@ -194,6 +216,9 @@ public class JdbcRepositoryCustomConversionIntegrationTests {
 		Date created;
 	}
 
+	record EntityWithDirections(@Id Long id, List<Direction> directions) {
+	}
+
 	enum Direction {
 		LEFT, CENTER, RIGHT
 	}

spring-data-jdbc/src/test/resources/org.springframework.data.jdbc.repository/JdbcRepositoryCustomConversionIntegrationTests-h2.sql

@@ -1,2 +1,3 @@
 CREATE TABLE ENTITY_WITH_STRINGY_BIG_DECIMAL ( id IDENTITY PRIMARY KEY, Stringy_number DECIMAL(20,10), DIRECTION INTEGER);
 CREATE TABLE OTHER_ENTITY ( ID IDENTITY PRIMARY KEY, CREATED DATE, ENTITY_WITH_STRINGY_BIG_DECIMAL INTEGER);
+CREATE TABLE ENTITY_WITH_DIRECTIONS ( ID IDENTITY PRIMARY KEY, DIRECTIONS INTEGER ARRAY);

spring-data-jdbc/src/test/resources/org.springframework.data.jdbc.repository/JdbcRepositoryCustomConversionIntegrationTests-hsql.sql

@@ -1,3 +1,4 @@
 CREATE TABLE ENTITY_WITH_STRINGY_BIG_DECIMAL ( id IDENTITY PRIMARY KEY, Stringy_number DECIMAL(20,10), DIRECTION INTEGER);
 CREATE TABLE OTHER_ENTITY ( ID IDENTITY PRIMARY KEY, CREATED DATE, ENTITY_WITH_STRINGY_BIG_DECIMAL INTEGER);
+CREATE TABLE ENTITY_WITH_DIRECTIONS ( ID IDENTITY PRIMARY KEY, DIRECTIONS INTEGER ARRAY);
 

spring-data-jdbc/src/test/resources/org.springframework.data.jdbc.repository/JdbcRepositoryCustomConversionIntegrationTests-postgres.sql

@@ -1,2 +1,3 @@
 CREATE TABLE ENTITY_WITH_STRINGY_BIG_DECIMAL ( id SERIAL PRIMARY KEY, Stringy_number DECIMAL(20,10), DIRECTION INTEGER);
 CREATE TABLE OTHER_ENTITY ( ID SERIAL PRIMARY KEY, CREATED DATE, ENTITY_WITH_STRINGY_BIG_DECIMAL INTEGER);
+CREATE TABLE ENTITY_WITH_DIRECTIONS ( ID SERIAL PRIMARY KEY, DIRECTIONS INTEGER ARRAY);

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

@@ -777,14 +777,35 @@ public class MappingRelationalConverter extends AbstractRelationalConverter
 		}
 
 		for (Object o : value) {
-			mapped.add(writeValue(o, component));
+			mapped.add(unwrap(writeValue(o, component)));
 		}
 
 		if (type.getType().isInstance(mapped) || !type.isCollectionLike()) {
 			return mapped;
 		}
 
-		return getConversionService().convert(mapped, type.getType());
+		// if we succeeded converting the members of the collection, we actually ignore the fallback targetType since that
+		// was derived without considering custom conversions.
+		Class<?> targetType = type.getType();
+		if (!mapped.isEmpty()) {
+
+			Class<?> targetComponentType = mapped.get(0).getClass();
+			targetType = Array.newInstance(targetComponentType, 0).getClass();
+		}
+		return getConversionService().convert(mapped, targetType);
+	}
+
+	/**
+	 * Unwraps technology specific wrappers. Custom conversions may choose to return a wrapper class that contains additional information for the technology driver.
+	 * These wrappers can't be used as members of a collection, therefore we may have to unwrap the values.
+	 *
+	 * This method allows technology specific implemenations to provide such an unwrapping mechanism.
+	 *
+	 * @param convertedValue a value that might need unwrapping.
+	 */
+	@Nullable
+	protected Object unwrap(@Nullable Object convertedValue) {
+		return convertedValue;
 	}
 
 	static Predicate<RelationalPersistentProperty> isConstructorArgument(PersistentEntity<?, ?> entity) {