Guard against Hibernate exposing non-embeddables as embeddables on versions > 5.4.21.

Hibernate 5.4.22 started including types managed by custom user types in the embeddables exposed via JPA's Metamodel API. This causes those to be considered types to explicitly map (read: unfold) in Spring Data REST. We now exposed a cleaned up view on this via a tweak in JpaPersistentPropertyImpl (ultimately in JpaMetamodel) looking for @Embeddable annotation on types allegedly considered embeddable by Hibernate.

Fixes #2421.

src/main/java/org/springframework/data/jpa/mapping/JpaPersistentPropertyImpl.java

@@ -109,7 +109,7 @@ class JpaPersistentPropertyImpl extends AnnotationBasedPersistentProperty<JpaPer
 
 		this.isIdProperty = Lazy.of(() -> ID_ANNOTATIONS.stream().anyMatch(it -> isAnnotationPresent(it)) //
 				|| metamodel.isSingleIdAttribute(getOwner().getType(), getName(), getType()));
-		this.isEntity = Lazy.of(() -> metamodel.isJpaManaged(getActualType()));
+		this.isEntity = Lazy.of(() -> metamodel.isMappedType(getActualType()));
 	}
 
 	/*

src/main/java/org/springframework/data/jpa/util/JpaMetamodel.java

@@ -16,15 +16,20 @@
 package org.springframework.data.jpa.util;
 
 import java.util.Collection;
+import java.util.EnumSet;
 import java.util.Map;
 import java.util.Optional;
+import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 
+import javax.persistence.Embeddable;
 import javax.persistence.metamodel.EntityType;
 import javax.persistence.metamodel.ManagedType;
 import javax.persistence.metamodel.Metamodel;
 import javax.persistence.metamodel.SingularAttribute;
+import javax.persistence.metamodel.Type.PersistenceType;
 
+import org.springframework.core.annotation.AnnotatedElementUtils;
 import org.springframework.data.util.Lazy;
 import org.springframework.data.util.StreamUtils;
 import org.springframework.util.Assert;
@@ -39,10 +44,13 @@ import org.springframework.util.Assert;
 public class JpaMetamodel {
 
 	private static final Map<Metamodel, JpaMetamodel> CACHE = new ConcurrentHashMap<>(4);
+	private static final Set<PersistenceType> ENTITY_OR_MAPPED_SUPERCLASS = EnumSet.of(PersistenceType.ENTITY,
+			PersistenceType.MAPPED_SUPERCLASS);
 
 	private final Metamodel metamodel;
 
 	private Lazy<Collection<Class<?>>> managedTypes;
+	private Lazy<Collection<Class<?>>> jpaEmbeddables;
 
 	/**
 	 * Creates a new {@link JpaMetamodel} for the given JPA {@link Metamodel}.
@@ -54,10 +62,17 @@ public class JpaMetamodel {
 		Assert.notNull(metamodel, "Metamodel must not be null!");
 
 		this.metamodel = metamodel;
+
 		this.managedTypes = Lazy.of(() -> metamodel.getManagedTypes().stream() //
 				.map(ManagedType::getJavaType) //
 				.filter(it -> it != null) //
 				.collect(StreamUtils.toUnmodifiableSet()));
+
+		this.jpaEmbeddables = Lazy.of(() -> metamodel.getEmbeddables().stream() //
+				.map(ManagedType::getJavaType)
+				.filter(it -> it != null)
+				.filter(it -> AnnotatedElementUtils.isAnnotated(it, Embeddable.class))
+				.collect(StreamUtils.toUnmodifiableSet()));
 	}
 
 	public static JpaMetamodel of(Metamodel metamodel) {
@@ -96,6 +111,27 @@ public class JpaMetamodel {
 				.orElse(false);
 	}
 
+	/**
+	 * Returns whether the given type is considered a mapped type, i.e. an actually JPA persisted entity, mapped
+	 * superclass or native JPA embeddable.
+	 *
+	 * @param entity must not be {@literal null}.
+	 * @return
+	 */
+	public boolean isMappedType(Class<?> entity) {
+
+		Assert.notNull(entity, "Type must not be null!");
+
+		if (!isJpaManaged(entity)) {
+			return false;
+		}
+
+		ManagedType<?> managedType = metamodel.managedType(entity);
+
+		return !managedType.getPersistenceType().equals(PersistenceType.EMBEDDABLE)
+				|| jpaEmbeddables.get().contains(entity);
+	}
+
 	/**
 	 * Wipes the static cache of {@link Metamodel} to {@link JpaMetamodel}.
 	 */

src/test/java/org/springframework/data/jpa/util/JpaMetamodelUnitTests.java

@@ -18,10 +18,17 @@ package org.springframework.data.jpa.util;
 import static org.assertj.core.api.Assertions.*;
 import static org.mockito.Mockito.*;
 
+import java.util.Arrays;
 import java.util.Collections;
+import java.util.HashSet;
 
+import javax.persistence.Embeddable;
+import javax.persistence.Entity;
+import javax.persistence.metamodel.EmbeddableType;
 import javax.persistence.metamodel.EntityType;
+import javax.persistence.metamodel.ManagedType;
 import javax.persistence.metamodel.Metamodel;
+import javax.persistence.metamodel.Type.PersistenceType;
 
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
@@ -60,4 +67,54 @@ class JpaMetamodelUnitTests {
 		JpaMetamodel.clear();
 		assertThat(model).isNotEqualTo(JpaMetamodel.of(metamodel));
 	}
+
+	@Test // #2421
+	void doesNotConsiderNonNativeEmbeddablesJpaManaged() {
+
+		JpaMetamodel model = JpaMetamodel.of(metamodel);
+
+		ManagedType<?> entity = getEntity(Wrapper.class);
+		ManagedType<?> embeddable = getEmbeddable(ExplicitEmbeddable.class);
+		ManagedType<?> inner = getEmbeddable(Inner.class);
+
+		doReturn(new HashSet<>(Arrays.asList(entity, embeddable, inner))).when(metamodel).getManagedTypes();
+		doReturn(new HashSet<>(Arrays.asList(embeddable, inner))).when(metamodel).getEmbeddables();
+
+		assertThat(model.isMappedType(Wrapper.class)).isTrue();
+		assertThat(model.isMappedType(ExplicitEmbeddable.class)).isTrue();
+		assertThat(model.isMappedType(Inner.class)).isFalse();
+	}
+
+	private EmbeddableType<?> getEmbeddable(Class<?> type) {
+
+		EmbeddableType<?> managedType = getManagedType(type, EmbeddableType.class);
+		doReturn(PersistenceType.EMBEDDABLE).when(managedType).getPersistenceType();
+
+		return managedType;
+	}
+
+	private EntityType<?> getEntity(Class<?> type) {
+
+		EntityType<?> managedType = getManagedType(type, EntityType.class);
+		doReturn(PersistenceType.ENTITY).when(managedType).getPersistenceType();
+
+		return managedType;
+	}
+
+	private <T extends ManagedType<?>> T getManagedType(Class<?> type, Class<T> baseType) {
+
+		T managedType = mock(baseType);
+		doReturn(type).when(managedType).getJavaType();
+		doReturn(managedType).when(metamodel).managedType(type);
+
+		return managedType;
+	}
+
+	@Entity
+	static class Wrapper {}
+
+	@Embeddable
+	static class ExplicitEmbeddable {}
+
+	static class Inner {}
 }