Read DTO projection properties only once.

We ensure to not read DTO properties multiple times if these are already read by their persistence creator.

Closes #4626

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/MappingMongoConverter.java

@@ -363,13 +363,6 @@ public class MappingMongoConverter extends AbstractMongoConverter implements App
 
 		populateProperties(context, mappedEntity, documentAccessor, evaluator, instance);
 
-		PersistentPropertyAccessor<?> convertingAccessor = new ConvertingPropertyAccessor<>(accessor, conversionService);
-		MongoDbPropertyValueProvider valueProvider = new MongoDbPropertyValueProvider(context, documentAccessor, evaluator,
-				spELContext);
-
-		readProperties(context, mappedEntity, convertingAccessor, documentAccessor, valueProvider, evaluator,
-				Predicates.isTrue());
-
 		return accessor.getBean();
 	}
 
@@ -506,16 +499,16 @@ public class MappingMongoConverter extends AbstractMongoConverter implements App
 		EntityInstantiator instantiator = instantiators.getInstantiatorFor(entity);
 		S instance = instantiator.createInstance(entity, provider);
 
-		if (entity.requiresPropertyPopulation()) {
 		return populateProperties(context, entity, documentAccessor, evaluator, instance);
 	}
 
-		return instance;
-	}
-
 	private <S> S populateProperties(ConversionContext context, MongoPersistentEntity<S> entity,
 			DocumentAccessor documentAccessor, SpELExpressionEvaluator evaluator, S instance) {
 
+		if (!entity.requiresPropertyPopulation()) {
+			return instance;
+		}
+
 		PersistentPropertyAccessor<S> accessor = new ConvertingPropertyAccessor<>(entity.getPropertyAccessor(instance),
 				conversionService);
 
@@ -566,7 +559,9 @@ public class MappingMongoConverter extends AbstractMongoConverter implements App
 		String expression = idProperty.getSpelExpression();
 		Object resolvedValue = expression != null ? evaluator.evaluate(expression) : rawId;
 
-		return resolvedValue != null ? readValue(context.forProperty(idProperty), resolvedValue, idProperty.getTypeInformation()) : null;
+		return resolvedValue != null
+				? readValue(context.forProperty(idProperty), resolvedValue, idProperty.getTypeInformation())
+				: null;
 	}
 
 	private void readProperties(ConversionContext context, MongoPersistentEntity<?> entity,
@@ -622,9 +617,8 @@ public class MappingMongoConverter extends AbstractMongoConverter implements App
 	}
 
 	@Nullable
-	private Object readAssociation(Association<MongoPersistentProperty> association,
-			DocumentAccessor documentAccessor, DbRefProxyHandler handler, DbRefResolverCallback callback,
-			ConversionContext context) {
+	private Object readAssociation(Association<MongoPersistentProperty> association, DocumentAccessor documentAccessor,
+			DbRefProxyHandler handler, DbRefResolverCallback callback, ConversionContext context) {
 
 		MongoPersistentProperty property = association.getInverse();
 		Object value = documentAccessor.get(property);
@@ -2426,8 +2420,6 @@ public class MappingMongoConverter extends AbstractMongoConverter implements App
 			this.returnedTypeDescriptor = projection;
 		}
 
-
-
 		@Override
 		public ConversionContext forProperty(String name) {
 

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/MappingMongoConverterUnitTests.java

@@ -28,11 +28,14 @@ import lombok.RequiredArgsConstructor;
 import java.math.BigDecimal;
 import java.math.BigInteger;
 import java.net.URL;
+import java.nio.ByteBuffer;
 import java.time.LocalDate;
 import java.time.LocalDateTime;
 import java.time.temporal.ChronoUnit;
 import java.util.*;
 
+import org.assertj.core.data.Percentage;
+import org.bson.BsonUndefined;
 import org.bson.types.Binary;
 import org.bson.types.Code;
 import org.bson.types.Decimal128;
@@ -125,7 +128,8 @@ class MappingMongoConverterUnitTests {
 	@BeforeEach
 	void beforeEach() {
 
-		MongoCustomConversions conversions = new MongoCustomConversions();
+		MongoCustomConversions conversions = new MongoCustomConversions(
+				Arrays.asList(new ByteBufferToDoubleHolderConverter()));
 
 		mappingContext = new MongoMappingContext();
 		mappingContext.setApplicationContext(context);
@@ -2531,8 +2535,8 @@ class MappingMongoConverterUnitTests {
 		converter.afterPropertiesSet();
 
 		org.bson.Document source = new org.bson.Document("typeImplementingMap",
-				new org.bson.Document("1st", "one").append("2nd", 2)).append("_class",
-						TypeWrappingTypeImplementingMap.class.getName());
+				new org.bson.Document("1st", "one").append("2nd", 2))
+				.append("_class", TypeWrappingTypeImplementingMap.class.getName());
 
 		TypeWrappingTypeImplementingMap target = converter.read(TypeWrappingTypeImplementingMap.class, source);
 
@@ -2720,8 +2724,8 @@ class MappingMongoConverterUnitTests {
 						.and((target, underlyingType) -> !converter.conversions.isSimpleType(target)),
 				mappingContext);
 
-		EntityProjection<WithNestedInterfaceProjection, Person> projection = introspector.introspect(WithNestedInterfaceProjection.class,
-				Person.class);
+		EntityProjection<WithNestedInterfaceProjection, Person> projection = introspector
+				.introspect(WithNestedInterfaceProjection.class, Person.class);
 		WithNestedInterfaceProjection person = converter.project(projection, source);
 
 		assertThat(person.getFirstname()).isEqualTo("spring");
@@ -2739,14 +2743,35 @@ class MappingMongoConverterUnitTests {
 						.and((target, underlyingType) -> !converter.conversions.isSimpleType(target)),
 				mappingContext);
 
-		EntityProjection<WithNestedDtoProjection, Person> projection = introspector.introspect(WithNestedDtoProjection.class,
-				Person.class);
+		EntityProjection<WithNestedDtoProjection, Person> projection = introspector
+				.introspect(WithNestedDtoProjection.class, Person.class);
 		WithNestedDtoProjection person = converter.project(projection, source);
 
 		assertThat(person.getFirstname()).isEqualTo("spring");
 		assertThat(person.getAddress().getStreet()).isEqualTo("data");
 	}
 
+	@Test // GH-4626
+	void projectShouldReadDtoProjectionPropertiesOnlyOnce() {
+
+		ByteBuffer number = ByteBuffer.allocate(8);
+		number.putDouble(1.2d);
+		number.flip();
+
+		org.bson.Document source = new org.bson.Document("number", number);
+
+		EntityProjectionIntrospector introspector = EntityProjectionIntrospector.create(converter.getProjectionFactory(),
+				EntityProjectionIntrospector.ProjectionPredicate.typeHierarchy()
+						.and((target, underlyingType) -> !converter.conversions.isSimpleType(target)),
+				mappingContext);
+
+		EntityProjection<DoubleHolderDto, WithDoubleHolder> projection = introspector.introspect(DoubleHolderDto.class,
+				WithDoubleHolder.class);
+		DoubleHolderDto result = converter.project(projection, source);
+
+		assertThat(result.number.number).isCloseTo(1.2, Percentage.withPercentage(1));
+	}
+
 	@Test // GH-2860
 	void projectShouldReadProjectionWithNestedEntity() {
 
@@ -3022,11 +3047,13 @@ class MappingMongoConverterUnitTests {
 
 	interface WithNestedInterfaceProjection {
 		String getFirstname();
+
 		AddressProjection getAddress();
 	}
 
 	interface WithNestedDtoProjection {
 		String getFirstname();
+
 		AddressDto getAddress();
 	}
 
@@ -3925,4 +3952,30 @@ class MappingMongoConverterUnitTests {
 		ComplexId id;
 		String value;
 	}
+
+	@ReadingConverter
+	static class ByteBufferToDoubleHolderConverter implements Converter<ByteBuffer, DoubleHolder> {
+
+		@Override
+		public DoubleHolder convert(ByteBuffer source) {
+			return new DoubleHolder(source.getDouble());
+		}
+	}
+
+	record DoubleHolder(double number) {
+
+	}
+
+	static class WithDoubleHolder {
+		DoubleHolder number;
+	}
+
+	static class DoubleHolderDto {
+		DoubleHolder number;
+
+		public DoubleHolderDto(DoubleHolder number) {
+			this.number = number;
+		}
+	}
+
 }