Read properties for DTO projections only once.

We now skip property population for properties that are populated through an entity creator (constructor/factory method).

Closes #1725

Author: mp911de

spring-data-r2dbc/src/test/java/org/springframework/data/r2dbc/core/R2dbcEntityTemplateUnitTests.java

@@ -29,6 +29,7 @@
 import reactor.core.publisher.Mono;
 import reactor.test.StepVerifier;
 
+import java.nio.ByteBuffer;
 import java.time.LocalDateTime;
 import java.util.ArrayList;
 import java.util.Collections;
@@ -43,6 +44,7 @@
 import org.springframework.data.annotation.LastModifiedDate;
 import org.springframework.data.annotation.Version;
 import org.springframework.data.auditing.ReactiveIsNewAwareAuditingHandler;
+import org.springframework.data.convert.ReadingConverter;
 import org.springframework.data.domain.Sort;
 import org.springframework.data.mapping.callback.ReactiveEntityCallbacks;
 import org.springframework.data.mapping.context.PersistentEntities;
@@ -91,7 +93,7 @@ void before() {
 				.bindMarkers(PostgresDialect.INSTANCE.getBindMarkersFactory()).build();
 
 		R2dbcCustomConversions conversions = R2dbcCustomConversions.of(PostgresDialect.INSTANCE, new MoneyConverter(),
-				new RowConverter(), new RowDocumentConverter());
+				new RowConverter(), new RowDocumentConverter(), new PkConverter());
 
 		entityTemplate = new R2dbcEntityTemplate(client, PostgresDialect.INSTANCE,
 				new MappingR2dbcConverter(new R2dbcMappingContext(), conversions));
@@ -632,6 +634,53 @@ void shouldConsiderRowConverter() {
 				}).verifyComplete();
 	}
 
+	@Test // GH-1725
+	void projectDtoShouldReadPropertiesOnce() {
+
+		MockRowMetadata metadata = MockRowMetadata.builder()
+				.columnMetadata(MockColumnMetadata.builder().name("number").type(R2dbcType.BINARY).build()).build();
+
+		ByteBuffer byteBuffer = ByteBuffer.allocate(8);
+		byteBuffer.putDouble(1.2);
+		byteBuffer.flip();
+
+		MockResult result = MockResult.builder()
+				.row(MockRow.builder().identified("number", Object.class, byteBuffer).metadata(metadata).build()).build();
+
+		recorder.addStubbing(s -> s.startsWith("SELECT"), result);
+
+		entityTemplate.select(WithDoubleHolder.class).as(DoubleHolderProjection.class).all().as(StepVerifier::create) //
+				.assertNext(actual -> {
+					assertThat(actual.number.number).isCloseTo(1.2d, withinPercentage(1d));
+				}).verifyComplete();
+	}
+
+	@ReadingConverter
+	static class PkConverter implements Converter<ByteBuffer, DoubleHolder> {
+
+		@Nullable
+		@Override
+		public DoubleHolder convert(ByteBuffer source) {
+			return new DoubleHolder(source.getDouble());
+		}
+	}
+
+	static class WithDoubleHolder {
+		DoubleHolder number;
+	}
+
+	static class DoubleHolderProjection {
+		DoubleHolder number;
+
+		public DoubleHolderProjection(DoubleHolder number) {
+			this.number = number;
+		}
+	}
+
+	record DoubleHolder(double number) {
+
+	}
+
 	@Test // GH-1696
 	void shouldConsiderRowDocumentConverter() {
 

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

@@ -238,17 +238,8 @@ String getColumnName(RelationalPersistentProperty prop) {
 
 		EntityInstantiator instantiator = getEntityInstantiators().getInstantiatorFor(mappedEntity);
 		R instance = instantiator.createInstance(mappedEntity, provider);
-		PersistentPropertyAccessor<R> accessor = mappedEntity.getPropertyAccessor(instance);
 
-		populateProperties(context, mappedEntity, documentAccessor, evaluator, instance);
-
-		PersistentPropertyAccessor<?> convertingAccessor = new ConvertingPropertyAccessor<>(accessor,
-				getConversionService());
-		RelationalPropertyValueProvider valueProvider = newValueProvider(documentAccessor, evaluator, context);
-
-		readProperties(context, mappedEntity, convertingAccessor, documentAccessor, valueProvider, Predicates.isTrue());
-
-		return accessor.getBean();
+		return populateProperties(context, mappedEntity, documentAccessor, evaluator, instance);
 	}
 
 	private Object doReadOrProject(ConversionContext context, RowDocument source, TypeInformation<?> typeHint,
@@ -452,11 +443,7 @@ private <S> S read(ConversionContext context, RelationalPersistentEntity<S> enti
 		EntityInstantiator instantiator = getEntityInstantiators().getInstantiatorFor(entity);
 		S instance = instantiator.createInstance(entity, provider);
 
-		if (entity.requiresPropertyPopulation()) {
-			return populateProperties(context, entity, documentAccessor, evaluator, instance);
-		}
-
-		return instance;
+		return populateProperties(context, entity, documentAccessor, evaluator, instance);
 	}
 
 	@Override
@@ -509,6 +496,10 @@ public RelationalPropertyValueProvider withContext(ConversionContext context) {
 	private <S> S populateProperties(ConversionContext context, RelationalPersistentEntity<S> entity,
 			RowDocumentAccessor documentAccessor, SpELExpressionEvaluator evaluator, S instance) {
 
+		if (!entity.requiresPropertyPopulation()) {
+			return instance;
+		}
+
 		PersistentPropertyAccessor<S> accessor = new ConvertingPropertyAccessor<>(entity.getPropertyAccessor(instance),
 				getConversionService());