Support for jMolecules' @Identity annotation.

Fixes #2438
Original pull request: #2439.

Author: odrotbohm

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

@@ -40,6 +40,7 @@
 import org.springframework.data.util.ClassTypeInformation;
 import org.springframework.data.util.Lazy;
 import org.springframework.data.util.Optionals;
+import org.springframework.data.util.ReflectionUtils;
 import org.springframework.data.util.StreamUtils;
 import org.springframework.data.util.TypeInformation;
 import org.springframework.lang.Nullable;
@@ -56,6 +57,7 @@ public abstract class AnnotationBasedPersistentProperty<P extends PersistentProp
 		extends AbstractPersistentProperty<P> {
 
 	private static final String SPRING_DATA_PACKAGE = "org.springframework.data";
+	private static final Class<? extends Annotation> IDENTITY_TYPE = loadIdentityType();
 
 	private final @Nullable String value;
 	private final Map<Class<? extends Annotation>, Optional<? extends Annotation>> annotationCache = new ConcurrentHashMap<>();
@@ -74,7 +76,8 @@ public abstract class AnnotationBasedPersistentProperty<P extends PersistentProp
 			.of(() -> !isTransient() && !isAnnotationPresent(ReadOnlyProperty.class));
 	private final Lazy<Boolean> isReference = Lazy.of(() -> !isTransient() //
 			&& (isAnnotationPresent(Reference.class) || super.isAssociation()));
-	private final Lazy<Boolean> isId = Lazy.of(() -> isAnnotationPresent(Id.class));
+	private final Lazy<Boolean> isId = Lazy
+			.of(() -> isAnnotationPresent(Id.class) || IDENTITY_TYPE != null && isAnnotationPresent(IDENTITY_TYPE));
 	private final Lazy<Boolean> isVersion = Lazy.of(() -> isAnnotationPresent(Version.class));
 	private final Lazy<TypeInformation<?>> associationTargetType = Lazy.of(() -> {
 
@@ -329,4 +332,19 @@ private Stream<? extends AnnotatedElement> getAccessors() {
 		return Optionals.toStream(Optional.ofNullable(getGetter()), Optional.ofNullable(getSetter()),
 				Optional.ofNullable(getField()));
 	}
+
+	/**
+	 * Load jMolecules' {@code @Identity} type if present on the classpath. Dedicated method instead of a simple static
+	 * initializer to be able to suppress the compiler warning.
+	 *
+	 * @return can be {@literal null}.
+	 */
+	@Nullable
+	@SuppressWarnings("unchecked")
+	private static Class<? extends Annotation> loadIdentityType() {
+
+		return (Class<? extends Annotation>) ReflectionUtils.loadIfPresent(
+				"org.jmolecules.ddd.annotation.Identity",
+				AbstractPersistentProperty.class.getClassLoader());
+	}
 }

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

@@ -28,6 +28,7 @@
 import java.util.stream.Stream;
 
 import org.assertj.core.api.ClassAssert;
+import org.jmolecules.ddd.annotation.Identity;
 import org.jmolecules.ddd.types.AggregateRoot;
 import org.jmolecules.ddd.types.Association;
 import org.jmolecules.ddd.types.Identifier;
@@ -329,6 +330,14 @@ void exposesAssociationTargetClassAsPersistentEntityType() {
 				.allMatch(it -> it.equals(ClassTypeInformation.from(Sample.class)));
 	}
 
+	@Test // #2438
+	void detectsJMoleculesIdentity() {
+
+		SamplePersistentProperty property = getProperty(JMolecules.class, "identifier");
+
+		assertThat(property.isIdProperty()).isTrue();
+	}
+
 	@SuppressWarnings("unchecked")
 	private Map<Class<? extends Annotation>, Annotation> getAnnotationCache(SamplePersistentProperty property) {
 		return (Map<Class<? extends Annotation>, Annotation>) ReflectionTestUtils.getField(property, "annotationCache");
@@ -515,6 +524,7 @@ interface NoField {
 	}
 
 	static class JMolecules {
+		@Identity Long identifier;
 		Association<JMoleculesAggregate, Identifier> association;
 	}