Fix KotlinCopyMethod detection for single-association property classes.

KotlinCopyMethod.shouldUsePublicCopyMethod(…) now considers single-association arrangements. Also, the method now early exists if pre-conditions aren't met.

Closes #3131

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

@@ -38,6 +38,7 @@ import java.util.stream.Collectors;
 import org.springframework.core.ResolvableType;
 import org.springframework.data.mapping.PersistentEntity;
 import org.springframework.data.mapping.PersistentProperty;
+import org.springframework.data.mapping.SimpleAssociationHandler;
 import org.springframework.data.mapping.SimplePropertyHandler;
 import org.springframework.data.util.KotlinReflectionUtils;
 import org.springframework.util.Assert;
@@ -158,8 +159,9 @@ class KotlinCopyMethod {
 
 		List<PersistentProperty<?>> persistentProperties = new ArrayList<>();
 		entity.doWithProperties((SimplePropertyHandler) persistentProperties::add);
+		entity.doWithAssociations((SimpleAssociationHandler) it -> persistentProperties.add(it.getInverse()));
 
-		if (persistentProperties.size() > 1) {
+		if (persistentProperties.size() != 1) {
 			return false;
 		}
 

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

@@ -25,6 +25,7 @@ import java.lang.reflect.Constructor;
 import java.util.function.Function;
 import java.util.stream.Stream;
 
+import org.jmolecules.ddd.types.Association;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 import org.springframework.beans.BeanUtils;
@@ -283,6 +284,27 @@ public class KotlinPropertyAccessorFactoryTests {
 		propertyAccessor.setProperty(createdBy, BeanUtils.instantiateClass(declaredConstructor, "baz"));
 	}
 
+	@MethodSource("factories")
+	@ParameterizedTest // GH-3131
+	void shouldApplyCopyForSinglePropertyClass(PersistentPropertyAccessorFactory factory) {
+
+		BasicPersistentEntity<Object, SamplePersistentProperty> entity = mappingContext
+				.getRequiredPersistentEntity(DataClassWithAssociation.class);
+
+		var foo = Association.forAggregate(new DataClassAggregate(new DataClassId("foo")));
+		var bar = Association.forAggregate(new DataClassAggregate(new DataClassId("bar")));
+		Object instance = createInstance(entity, parameter -> foo);
+
+		var propertyAccessor = factory.getPropertyAccessor(entity, instance);
+		var persistentProperty = entity.getRequiredPersistentProperty("assoc");
+
+		assertThat(propertyAccessor).isNotNull();
+		assertThat(propertyAccessor.getProperty(persistentProperty)).isEqualTo(foo);
+
+		propertyAccessor.setProperty(persistentProperty, bar);
+		assertThat(propertyAccessor.getProperty(persistentProperty)).isEqualTo(bar);
+	}
+
 	private Object createInstance(BasicPersistentEntity<?, SamplePersistentProperty> entity,
 			Function<Parameter<?, ?>, Object> parameterProvider) {
 		return instantiators.getInstantiatorFor(entity).createInstance(entity,

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

@@ -15,6 +15,8 @@
  */
 package org.springframework.data.mapping.model
 
+import org.jmolecules.ddd.types.AggregateRoot
+import org.jmolecules.ddd.types.Identifier
 import org.springframework.data.annotation.Id
 import java.time.LocalDateTime
 
@@ -36,6 +38,19 @@ data class DataClassWithLazy(
 	val foo by lazy { 123 }
 }
 
+data class DataClassWithAssociation(
+	val assoc: org.jmolecules.ddd.types.Association<DataClassAggregate, DataClassId>
+)
+
+data class DataClassId(val id: String) : Identifier {
+
+}
+
+data class DataClassAggregate(val identifier: DataClassId) :
+	AggregateRoot<DataClassAggregate, DataClassId> {
+	override fun getId() = this.identifier
+}
+
 data class SingleSettableProperty constructor(val id: Double = Math.random()) {
 	val version: Int? = null
 }