DATACMNS-89 - ChainingConverter now eagerly returns values.

The ChainingConverter now returns values as soon as one converter in the chain produces an instance that's compatible to the target type. This allows ResourceProcessor clients to provide a Converter to take care of the complete conversion themselves.

Author: odrotbohm

src/main/java/org/springframework/data/repository/query/ResultProcessor.java

@@ -127,7 +127,7 @@ public <T> T processResult(Object source, Converter<Object, Object> preparingCon
 
 		Assert.notNull(preparingConverter, "Preparing converter must not be null!");
 
-		ChainingConverter converter = ChainingConverter.of(preparingConverter).and(this.converter);
+		ChainingConverter converter = ChainingConverter.of(type.getReturnedType(), preparingConverter).and(this.converter);
 
 		if (source instanceof Page && method.isPageQuery()) {
 			return (T) ((Page<?>) source).map(converter);
@@ -151,6 +151,7 @@ public <T> T processResult(Object source, Converter<Object, Object> preparingCon
 	@RequiredArgsConstructor(staticName = "of")
 	private static class ChainingConverter implements Converter<Object, Object> {
 
+		private final @NonNull Class<?> targetType;
 		private final @NonNull Converter<Object, Object> delegate;
 
 		/**
@@ -164,11 +165,13 @@ public ChainingConverter and(final Converter<Object, Object> converter) {
 
 			Assert.notNull(converter, "Converter must not be null!");
 
-			return new ChainingConverter(new Converter<Object, Object>() {
+			return new ChainingConverter(targetType, new Converter<Object, Object>() {
 
 				@Override
 				public Object convert(Object source) {
-					return converter.convert(ChainingConverter.this.convert(source));
+
+					Object intermediate = ChainingConverter.this.convert(source);
+					return targetType.isInstance(intermediate) ? intermediate : converter.convert(intermediate);
 				}
 			});
 		}

src/test/java/org/springframework/data/repository/query/ResultProcessorUnitTests.java

@@ -28,6 +28,7 @@
 
 import org.junit.Test;
 import org.springframework.beans.factory.annotation.Value;
+import org.springframework.core.convert.converter.Converter;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.PageImpl;
 import org.springframework.data.domain.Pageable;
@@ -61,7 +62,7 @@ public void leavesNonProjectingResultUntouched() throws Exception {
 	@Test
 	public void createsProjectionFromProperties() throws Exception {
 
-		ResultProcessor information = getFactory("findOneProjection");
+		ResultProcessor information = getProcessor("findOneProjection");
 
 		SampleProjection result = information.processResult(Arrays.asList("Matthews"));
 
@@ -75,7 +76,7 @@ public void createsProjectionFromProperties() throws Exception {
 	@SuppressWarnings("unchecked")
 	public void createsListOfProjectionsFormNestedLists() throws Exception {
 
-		ResultProcessor information = getFactory("findAllProjection");
+		ResultProcessor information = getProcessor("findAllProjection");
 
 		List<String> columns = Arrays.asList("Matthews");
 		List<List<String>> source = new ArrayList<List<String>>(Arrays.asList(columns));
@@ -93,7 +94,7 @@ public void createsListOfProjectionsFormNestedLists() throws Exception {
 	@SuppressWarnings("unchecked")
 	public void createsListOfProjectionsFromMaps() throws Exception {
 
-		ResultProcessor information = getFactory("findAllProjection");
+		ResultProcessor information = getProcessor("findAllProjection");
 
 		List<Map<String, Object>> source = new ArrayList<Map<String, Object>>(
 				Arrays.asList(Collections.<String, Object> singletonMap("lastname", "Matthews")));
@@ -110,7 +111,7 @@ public void createsListOfProjectionsFromMaps() throws Exception {
 	@Test
 	public void createsListOfProjectionsFromEntity() throws Exception {
 
-		ResultProcessor information = getFactory("findAllProjection");
+		ResultProcessor information = getProcessor("findAllProjection");
 
 		List<Sample> source = new ArrayList<Sample>(Arrays.asList(new Sample("Dave", "Matthews")));
 		List<SampleProjection> result = information.processResult(source);
@@ -125,7 +126,7 @@ public void createsListOfProjectionsFromEntity() throws Exception {
 	@Test
 	public void createsPageOfProjectionsFromEntity() throws Exception {
 
-		ResultProcessor information = getFactory("findPageProjection", Pageable.class);
+		ResultProcessor information = getProcessor("findPageProjection", Pageable.class);
 
 		Page<Sample> source = new PageImpl<Sample>(Arrays.asList(new Sample("Dave", "Matthews")));
 		Page<SampleProjection> result = information.processResult(source);
@@ -140,7 +141,7 @@ public void createsPageOfProjectionsFromEntity() throws Exception {
 	@Test
 	public void createsDynamicProjectionFromEntity() throws Exception {
 
-		ResultProcessor information = getFactory("findOneOpenProjection");
+		ResultProcessor information = getProcessor("findOneOpenProjection");
 
 		OpenProjection result = information.processResult(new Sample("Dave", "Matthews"));
 
@@ -156,7 +157,7 @@ public void findsDynamicProjection() throws Exception {
 
 		ParameterAccessor accessor = mock(ParameterAccessor.class);
 
-		ResultProcessor factory = getFactory("findOneDynamic", Class.class);
+		ResultProcessor factory = getProcessor("findOneDynamic", Class.class);
 		assertThat(factory.withDynamicProjection(null), is(factory));
 		assertThat(factory.withDynamicProjection(accessor), is(factory));
 
@@ -166,7 +167,26 @@ public void findsDynamicProjection() throws Exception {
 		assertThat(processor.getReturnedType().getReturnedType(), is(typeCompatibleWith(SampleProjection.class)));
 	}
 
-	private static ResultProcessor getFactory(String methodName, Class<?>... parameters) throws Exception {
+	/**
+	 * @see DATACMNS-89
+	 */
+	@Test
+	public void refrainsFromProjectingIfThePreparingConverterReturnsACompatibleInstance() throws Exception {
+
+		ResultProcessor processor = getProcessor("findAllDtos");
+
+		Object result = processor.processResult(new Sample("Dave", "Matthews"), new Converter<Object, Object>() {
+
+			@Override
+			public Object convert(Object source) {
+				return new SampleDTO();
+			}
+		});
+
+		assertThat(result, is(instanceOf(SampleDTO.class)));
+	}
+
+	private static ResultProcessor getProcessor(String methodName, Class<?>... parameters) throws Exception {
 		return getQueryMethod(methodName, parameters).getResultProcessor();
 	}