Apply Kotlin Value Class unboxing to generated Property Accessors.

Unwrap wrapped value types if necessary when using generated property accessors.

Closes spring-projects#3087

Author: mp911de

src/main/java/org/springframework/data/mapping/model/ClassGeneratingPropertyAccessorFactory.java

@@ -1478,7 +1478,7 @@ static Function<Object, Object> getWrapper(PersistentProperty<?> property) {
 
 				Parameter parameter = copy.getParameters()[kotlinCopyByProperty.getParameterPosition()];
 
-				return o -> ClassUtils.isAssignableValue(parameter.getType(), o) || vh == null ? o : vh.wrap(o);
+				return o -> ClassUtils.isAssignableValue(parameter.getType(), o) || vh == null ? o : vh.applyWrapping(o);
 			}
 
 			return Function.identity();

src/main/java/org/springframework/data/mapping/model/KotlinValueUtils.java

@@ -33,6 +33,7 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
+import java.util.function.BiFunction;
 
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
@@ -200,6 +201,8 @@ static final class ValueBoxing {
 
 		private final KFunction<?> wrapperConstructor;
 
+		private final KProperty<?> valueProperty;
+
 		private final boolean applyBoxing;
 
 		private final @Nullable ValueBoxing next;
@@ -258,7 +261,6 @@ private ValueBoxing(BoxingRules rules, KType type, KClass<?> kClass, boolean opt
 			boolean applyBoxing;
 
 			if (kClass.isValue()) {
-
 				wrapperConstructor = kClass.getConstructors().iterator().next();
 				KParameter nested = wrapperConstructor.getParameters().get(0);
 				KType nestedType = nested.getType();
@@ -275,10 +277,12 @@ private ValueBoxing(BoxingRules rules, KType type, KClass<?> kClass, boolean opt
 				}
 
 				Assert.notNull(nestedClass, () -> String.format("Cannot resolve nested class from type %s", nestedType));
-
+				this.valueProperty = kClass.getMembers().stream().filter(it -> it instanceof KProperty<?>)
+						.map(KProperty.class::cast).findFirst().get();
 				next = new ValueBoxing(rules, nestedType, nestedClass, nested.isOptional());
 			} else {
 				applyBoxing = false;
+				this.valueProperty = null;
 			}
 
 			this.kClass = kClass;
@@ -373,20 +377,46 @@ public ValueBoxing getNext() {
 		}
 
 		/**
-		 * Apply wrapping into the boxing wrapper type if applicable.
+		 * Wrap the value into the boxing wrapper type if requested. Already wrapped values are left unchanged.
 		 *
 		 * @param o
 		 * @return
 		 */
 		@Nullable
 		public Object wrap(@Nullable Object o) {
+			return doWrap(o, false, ValueBoxing::wrap);
+		}
+
+		/**
+		 * Apply wrapping into the boxing wrapper type if applicable. For types, that do not require wrapping but are
+		 * wrapped, the component type is being unwrapped.
+		 *
+		 * @param o
+		 * @return
+		 * @since 3.2.6
+		 */
+		@Nullable
+		Object applyWrapping(@Nullable Object o) {
+			return doWrap(o, true, ValueBoxing::applyWrapping);
+		}
+
+		/**
+		 * Apply staged wrapping into the boxing wrapper type if value boxing is requested. Otherwise, apply unwrapping and
+		 * pass on the result into {@code nextWrapStage}.
+		 */
+		@Nullable
+		Object doWrap(@Nullable Object o, boolean unwrap, BiFunction<ValueBoxing, Object, Object> nextWrapStage) {
 
 			if (applyBoxing) {
-				return o == null || kClass.isInstance(o) ? o : wrapperConstructor.call(next.wrap(o));
+				return o == null || kClass.isInstance(o) ? o : wrapperConstructor.call(nextWrapStage.apply(next, o));
+			} else if (unwrap && kClass.isValue()) {
+				if (o != null && kClass.isInstance(o)) {
+					o = valueProperty.getGetter().call(o);
+				}
 			}
 
 			if (hasNext()) {
-				return next.wrap(o);
+				return nextWrapStage.apply(next, o);
 			}
 
 			return o;

src/test/java/org/springframework/data/mapping/model/KotlinPropertyAccessorFactoryTests.java

@@ -21,6 +21,7 @@
 import kotlin.reflect.KClass;
 import kotlin.reflect.jvm.internal.KotlinReflectionInternalError;
 
+import java.lang.reflect.Constructor;
 import java.util.function.Function;
 import java.util.stream.Stream;
 
@@ -255,6 +256,33 @@ void genericNullableInlineClassesShouldWork(PersistentPropertyAccessorFactory fa
 		assertThat(propertyAccessor.getProperty(recursive)).isEqualTo(newOuter);
 	}
 
+	@MethodSource("factories")
+	@ParameterizedTest // GH-1947
+	void shouldUnwrapValueTypeIfNecessary(PersistentPropertyAccessorFactory factory) throws Exception {
+
+		BasicPersistentEntity<Object, SamplePersistentProperty> entity = mappingContext
+				.getRequiredPersistentEntity(MyEntity.class);
+
+		Constructor<?> declaredConstructor = MyValueClass.class.getDeclaredConstructor(String.class);
+
+		Object instance = createInstance(entity, parameter -> {
+
+			String name = parameter.getName();
+
+			return switch (name) {
+				case "id" -> 1L;
+				case "name" -> "foo";
+				default -> "bar";
+			};
+
+		});
+
+		var propertyAccessor = factory.getPropertyAccessor(entity, instance);
+		var createdBy = entity.getRequiredPersistentProperty("createdBy");
+
+		propertyAccessor.setProperty(createdBy, BeanUtils.instantiateClass(declaredConstructor, "baz"));
+	}
+
 	private Object createInstance(BasicPersistentEntity<?, SamplePersistentProperty> entity,
 			Function<Parameter<?, ?>, Object> parameterProvider) {
 		return instantiators.getInstantiatorFor(entity).createInstance(entity,

src/test/kotlin/org/springframework/data/mapping/model/InlineClasses.kt

@@ -58,6 +58,12 @@ value class MyGenericValue<T>(val id: T)
 @JvmInline
 value class MyGenericBoundValue<T : CharSequence>(val id: T)
 
+data class MyEntity(
+	val id: Long = 0L,
+	val name: String,
+	val createdBy: MyValueClass = MyValueClass("UNKNOWN"),
+)
+
 data class WithGenericValue(
 	// ctor: WithGenericValue(CharSequence string, CharSequence charseq, Object recursive, DefaultConstructorMarker $constructor_marker)
 	val string: MyGenericBoundValue<String>,