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 #1472

Author: mp911de

spring-data-cassandra/src/main/java/org/springframework/data/cassandra/core/convert/MappingCassandraConverter.java

@@ -346,11 +346,15 @@ private <R> R doReadProjection(ConversionContext context, CassandraValueProvider
 
 		EntityInstantiator instantiator = instantiators.getInstantiatorFor(mappedEntity);
 		R instance = instantiator.createInstance(mappedEntity, provider);
-		PersistentPropertyAccessor<R> accessor = mappedEntity.getPropertyAccessor(instance);
 
-		readProperties(context, mappedEntity, valueProviderToUse, accessor, Predicates.isTrue());
+		if (mappedEntity.requiresPropertyPopulation()) {
 
-		return accessor.getBean();
+			PersistentPropertyAccessor<R> accessor = mappedEntity.getPropertyAccessor(instance);
+			readProperties(context, mappedEntity, valueProviderToUse, accessor, isConstructorArgument(mappedEntity).negate());
+			return accessor.getBean();
+		}
+
+		return instance;
 	}
 
 	private Object doReadOrProject(ConversionContext context, Row row, TypeInformation<?> typeHint,
@@ -515,14 +519,19 @@ private <S> S doReadEntity(ConversionContext context, CassandraValueProvider val
 		EntityInstantiator instantiator = this.instantiators.getInstantiatorFor(entity);
 		S instance = instantiator.createInstance(entity, provider);
 
-		if (entity.requiresPropertyPopulation()) {
-			ConvertingPropertyAccessor<S> propertyAccessor = newConvertingPropertyAccessor(instance, entity);
+		return populateProperties(context, entity, valueProvider, instance);
+	}
+
+	private <S> S populateProperties(ConversionContext context, CassandraPersistentEntity<?> entity,
+			CassandraValueProvider valueProvider, S instance) {
 
-			readProperties(context, entity, valueProvider, propertyAccessor, isConstructorArgument(entity).negate());
-			return propertyAccessor.getBean();
+		if (!entity.requiresPropertyPopulation()) {
+			return instance;
 		}
 
-		return instance;
+		ConvertingPropertyAccessor<S> propertyAccessor = newConvertingPropertyAccessor(instance, entity);
+		readProperties(context, entity, valueProvider, propertyAccessor, isConstructorArgument(entity).negate());
+		return propertyAccessor.getBean();
 	}
 
 	private void readProperties(ConversionContext context, CassandraPersistentEntity<?> entity,
@@ -1437,7 +1446,7 @@ public <T> T getParameterValue(Parameter<T, CassandraPersistentProperty> paramet
 
 	}
 
-	private record PropertyTranslatingPropertyAccessor<T> (PersistentPropertyAccessor<T> delegate,
+	private record PropertyTranslatingPropertyAccessor<T>(PersistentPropertyAccessor<T> delegate,
 			PersistentPropertyTranslator propertyTranslator) implements PersistentPropertyAccessor<T> {
 
 		static <T> PersistentPropertyAccessor<T> create(PersistentPropertyAccessor<T> delegate,

spring-data-cassandra/src/test/java/org/springframework/data/cassandra/core/convert/MappingCassandraConverterUnitTests.java

@@ -24,13 +24,15 @@
 import java.math.BigInteger;
 import java.net.InetAddress;
 import java.net.UnknownHostException;
+import java.nio.ByteBuffer;
 import java.time.Instant;
 import java.time.LocalDate;
 import java.time.LocalDateTime;
 import java.time.ZoneId;
 import java.time.ZoneOffset;
 import java.util.*;
 
+import org.assertj.core.data.Percentage;
 import org.json.simple.JSONObject;
 import org.json.simple.parser.JSONParser;
 import org.json.simple.parser.ParseException;
@@ -55,6 +57,7 @@
 import org.springframework.data.cassandra.domain.UserToken;
 import org.springframework.data.cassandra.support.UserDefinedTypeBuilder;
 import org.springframework.data.cassandra.test.util.RowMockUtil;
+import org.springframework.data.convert.ReadingConverter;
 import org.springframework.data.convert.SimplePropertyValueConversions;
 import org.springframework.data.convert.ValueConverter;
 import org.springframework.data.projection.EntityProjection;
@@ -88,9 +91,13 @@ public class MappingCassandraConverterUnitTests {
 	@BeforeEach
 	void setUp() {
 
+		CassandraCustomConversions conversions = new CassandraCustomConversions(
+				List.of(new ByteBufferToDoubleHolderConverter()));
 		this.mappingContext = new CassandraMappingContext();
+		this.mappingContext.setSimpleTypeHolder(conversions.getSimpleTypeHolder());
 
 		this.converter = new MappingCassandraConverter(mappingContext);
+		this.converter.setCustomConversions(conversions);
 		this.converter.afterPropertiesSet();
 	}
 
@@ -1074,6 +1081,27 @@ void shouldCreateDtoProjectionsThroughConstructor() {
 		assertThat(result.tuple().one).isEqualTo("One");
 	}
 
+	@Test // GH-1472
+	void projectShouldReadDtoProjectionPropertiesOnlyOnce() {
+
+		ByteBuffer number = ByteBuffer.allocate(8);
+		number.putDouble(1.2d);
+		number.flip();
+
+		rowMock = RowMockUtil.newRowMock(RowMockUtil.column("number", number, DataTypes.BLOB));
+
+		EntityProjectionIntrospector introspector = EntityProjectionIntrospector.create(
+				new SpelAwareProxyProjectionFactory(), EntityProjectionIntrospector.ProjectionPredicate.typeHierarchy(),
+				this.mappingContext);
+
+		EntityProjection<DoubleHolderDto, WithDoubleHolder> projection = introspector.introspect(DoubleHolderDto.class,
+				WithDoubleHolder.class);
+
+		DoubleHolderDto result = this.converter.project(projection, rowMock);
+
+		assertThat(result.number.number).isCloseTo(1.2, Percentage.withPercentage(1));
+	}
+
 	@Test // GH-1471
 	void propertyValueConversionsCacheShouldConsiderPropertyEquality() {
 
@@ -1770,4 +1798,29 @@ public void setLastName(String lastName) {
 			this.lastName = lastName;
 		}
 	}
+
+	@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;
+		}
+	}
 }