Persistent entity type detection now starts with the association target type if available.

This causes us to inspect the most concrete type we can find from a property declaration that might be overridden using an annotation.

Closes: #2409
Original Pull Request: #2410

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

@@ -436,9 +436,8 @@ public abstract class AbstractPersistentProperty<P extends PersistentProperty<P>
 
 	private Set<TypeInformation<?>> detectEntityTypes(SimpleTypeHolder simpleTypes) {
 
-		TypeInformation<?> typeToStartWith = ASSOCIATION_TYPE != null && ASSOCIATION_TYPE.isAssignableFrom(rawType)
-				? information.getComponentType()
-				: information;
+		TypeInformation<?> typeToStartWith = getAssociationTargetTypeInformation();
+		typeToStartWith = typeToStartWith == null ? information : typeToStartWith;
 
 		Set<TypeInformation<?>> result = detectEntityTypes(typeToStartWith);
 

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

@@ -47,6 +47,7 @@ import org.springframework.data.mapping.MappingException;
 import org.springframework.data.mapping.PersistentProperty;
 import org.springframework.data.mapping.context.SampleMappingContext;
 import org.springframework.data.mapping.context.SamplePersistentProperty;
+import org.springframework.data.util.ClassTypeInformation;
 import org.springframework.lang.Nullable;
 import org.springframework.test.util.ReflectionTestUtils;
 
@@ -318,6 +319,16 @@ public class AnnotationBasedPersistentPropertyUnitTests<P extends AnnotationBase
 		assertThat(property.getAssociationTargetType()).isEqualTo(JMoleculesAggregate.class);
 	}
 
+	@Test // GH-2409
+	void exposesAssociationTargetClassAsPersistentEntityType() {
+
+		SamplePersistentProperty property = getProperty(WithReferences.class, "toSample");
+
+		assertThat(property.getPersistentEntityTypeInformation()) //
+				.isNotEmpty() //
+				.allMatch(it -> it.equals(ClassTypeInformation.from(Sample.class)));
+	}
+
 	@SuppressWarnings("unchecked")
 	private Map<Class<? extends Annotation>, Annotation> getAnnotationCache(SamplePersistentProperty property) {
 		return (Map<Class<? extends Annotation>, Annotation>) ReflectionTestUtils.getField(property, "annotationCache");