HHH-16197 Circular references of the same entity result in different Java objects when caching is enabled and using a query

hibernate-core/src/main/java/org/hibernate/engine/spi/SharedSessionContractImplementor.java

@@ -341,6 +341,16 @@ public interface SharedSessionContractImplementor
 	 */
 	String bestGuessEntityName(Object object);
 
+	/**
+	 * Obtain the best estimate of the entity name of the given entity
+	 * instance, which is not involved in an association, by also
+	 * considering information held in the proxy, and whether the object
+	 * is already associated with this session.
+	 */
+	default String bestGuessEntityName(Object object, EntityEntry entry) {
+		return bestGuessEntityName( object );
+	}
+
 	/**
 	 * Obtain an estimate of the entity name of the given entity instance,
 	 * which is not involved in an association, using only the

hibernate-core/src/main/java/org/hibernate/event/internal/DefaultPersistEventListener.java

@@ -81,7 +81,7 @@ public class DefaultPersistEventListener
 	private void persist(PersistEvent event, PersistContext createCache, Object entity) {
 		final EventSource source = event.getSession();
 		final EntityEntry entityEntry = source.getPersistenceContextInternal().getEntry( entity );
-		final String entityName = entityName( event, entity );
+		final String entityName = entityName( event, entity, entityEntry );
 		switch ( entityState( event, entity, entityName, entityEntry ) ) {
 			case DETACHED:
 				throw new PersistentObjectException( "detached entity passed to persist: "
@@ -133,13 +133,13 @@ public class DefaultPersistEventListener
 		return entityState;
 	}
 
-	private static String entityName(PersistEvent event, Object entity) {
+	private static String entityName(PersistEvent event, Object entity, EntityEntry entityEntry) {
 		if ( event.getEntityName() != null ) {
 			return event.getEntityName();
 		}
 		else {
 			// changes event.entityName by side effect!
-			final String entityName = event.getSession().bestGuessEntityName( entity );
+			final String entityName = event.getSession().bestGuessEntityName( entity, entityEntry );
 			event.setEntityName( entityName );
 			return entityName;
 		}

hibernate-core/src/main/java/org/hibernate/internal/SessionImpl.java

@@ -1718,6 +1718,25 @@ public class SessionImpl
 		}
 	}
 
+	@Override
+	public String bestGuessEntityName(Object object, EntityEntry entry) {
+		final LazyInitializer lazyInitializer = extractLazyInitializer( object );
+		if ( lazyInitializer != null ) {
+			// it is possible for this method to be called during flush processing,
+			// so make certain that we do not accidentally initialize an uninitialized proxy
+			if ( lazyInitializer.isUninitialized() ) {
+				return lazyInitializer.getEntityName();
+			}
+			object = lazyInitializer.getImplementation();
+		}
+		if ( entry == null ) {
+			return guessEntityName( object );
+		}
+		else {
+			return entry.getPersister().getEntityName();
+		}
+	}
+
 	@Override
 	public String getEntityName(Object object) {
 		checkOpen();

hibernate-core/src/main/java/org/hibernate/sql/results/graph/entity/AbstractEntityInitializer.java

@@ -699,9 +699,9 @@ public abstract class AbstractEntityInitializer extends AbstractFetchParentAcces
 			preLoad( rowProcessingState );
 
 			final LazyInitializer lazyInitializer = extractLazyInitializer( entityInstance );
+			final SharedSessionContractImplementor session = rowProcessingState.getSession();
+			final PersistenceContext persistenceContext = session.getPersistenceContextInternal();
 			if ( lazyInitializer != null ) {
-				final SharedSessionContractImplementor session = rowProcessingState.getSession();
-				final PersistenceContext persistenceContext = session.getPersistenceContextInternal();
 				Object instance = persistenceContext.getEntity( entityKey );
 				if ( instance == null ) {
 					instance = resolveInstance(
@@ -715,8 +715,42 @@ public abstract class AbstractEntityInitializer extends AbstractFetchParentAcces
 				entityInstanceForNotify = instance;
 			}
 			else {
-				initializeEntity( entityInstance, rowProcessingState );
-				entityInstanceForNotify = entityInstance;
+				if ( entityDescriptor.canReadFromCache() ) {
+					/*
+						@Cache
+						class Child {
+
+							@ManyToOne
+							private Parent parent;
+						}
+
+						@Cache
+						class Parent {
+							@OneToOne
+							private Parent parent;
+
+						}
+
+						when the query "select c from Child c" is executed and the second level cache (2LC) contains
+						an instance of Child and Parent
+						then when the EntitySelectFetchInitializer#initializeInstance() is executed before the EntityResultInitializer one
+						the persistence context will contain the instances retrieved form the 2LC
+					 */
+					final Object entity = persistenceContext.getEntity( entityKey );
+					if ( entity != null ) {
+						entityInstance = entity;
+						registerLoadingEntity( rowProcessingState, entityInstance );
+						initializeEntityInstance( entityInstance, rowProcessingState );
+					}
+					else {
+						initializeEntity( entityInstance, rowProcessingState );
+					}
+					entityInstanceForNotify = entityInstance;
+				}
+				else {
+					initializeEntity( entityInstance, rowProcessingState );
+					entityInstanceForNotify = entityInstance;
+				}
 			}
 
 			notifyResolutionListeners( entityInstanceForNotify );