Jones ( https://hibernate.atlassian.net/secure/ViewProfile.jspa?accountId=557058%... ) *created* an issue Hibernate ORM ( https://hibernate.atlassian.net/browse/HHH?atlOrigin=eyJpIjoiZWFhZTY2NmVh... ) / Bug ( https://hibernate.atlassian.net/browse/HHH-16565?atlOrigin=eyJpIjoiZWFhZT... ) HHH-16565 ( https://hibernate.atlassian.net/browse/HHH-16565?atlOrigin=eyJpIjoiZWFhZT... ) ClassCastException when batch fetch and 2nd level cache are enabled for polymorphic entities ( https://hibernate.atlassian.net/browse/HHH-16565?atlOrigin=eyJpIjoiZWFhZT... ) Issue Type: Bug Affects Versions: 6.2.2 Assignee: Unassigned Created: 07/May/2023 22:11 PM Priority: Major Reporter: Jones ( https://hibernate.atlassian.net/secure/ViewProfile.jspa?accountId=557058%... ) Given * Batch fetch is enabled * 2nd Level cache is enabled * Polymorphic entity annotated with org.hibernate.annotations.Cache When * find entity by id using id from another type Then * ClassCastException occurs @Entity @Table(name = "THE_ENTITY" ) @DiscriminatorColumn(name = "DISC_COL" , discriminatorType = DiscriminatorType.INTEGER) @Cache(usage = CacheConcurrencyStrategy.READ_WRITE) public abstract class AbstractEntity { @Id @Column(name = "ID" ) Integer id; } @Entity @DiscriminatorValue( "1" ) public class EntityA extends AbstractEntity { } @Entity @DiscriminatorValue( "2" ) public class EntityB extends AbstractEntity { } @Override protected void configure(Configuration configuration) { super.configure(configuration); configuration.setProperty(AvailableSettings.SHOW_SQL, Boolean.TRUE.toString()); configuration.setProperty(AvailableSettings.FORMAT_SQL, Boolean.TRUE.toString()); configuration.setProperty(AvailableSettings.DEFAULT_BATCH_FETCH_SIZE, "10" ); configuration.setProperty(AvailableSettings.USE_SECOND_LEVEL_CACHE, Boolean.TRUE.toString()); configuration.setProperty(AvailableSettings.CACHE_REGION_FACTORY, JCacheRegionFactory. class. getName()); configuration.setProperty( "hibernate.javax.cache.provider" , EhcacheCachingProvider. class. getName()); } @Test public void hhhXXXXTest() throws Exception { Integer id = 123; try (Session s = openSession()) { Transaction tx = s.beginTransaction(); EntityA entityA = new EntityA(); entityA.id = id; s.persist(entityA); tx.commit(); } try (Session s = openSession()) { EntityA entityA = s.find(EntityA.class, id); assertThat(entityA.id).isEqualTo(id); } try (Session s = openSession()) { EntityB entityB = s.find(EntityB.class, id); assertThat(entityB).isNull(); } } java.lang.ClassCastException: class org.hibernate.bugs.EntityA cannot be cast to class org.hibernate.bugs.EntityB (org.hibernate.bugs.EntityA and org.hibernate.bugs.EntityB are in unnamed module of loader 'app') at org.hibernate.bugs.ORMUnitTestCase.hhhXXXXTest(ORMUnitTestCase.java:81) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77) at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.base/java.lang.reflect.Method.invoke(Method.java:568) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56) at org.hibernate.testing.junit4.ExtendedFrameworkMethod.invokeExplosively(ExtendedFrameworkMethod.java:45) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26) at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27) at org.junit.internal.runners.statements.FailOnTimeout$CallableStatement.call(FailOnTimeout.java:299) at org.junit.internal.runners.statements.FailOnTimeout$CallableStatement.call(FailOnTimeout.java:293) at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) at java.base/java.lang.Thread.run(Thread.java:833) Some notes: * This issue doesn’t happen in latest hibernate 5.6.x * Disabling 2nd level cache avoids the issue * Disabling batch fetch also avoids the issue Although trying to find EntityB with EntityA id could be considered an application/logic bug by itself, I would expect hibernate to have a consistent behaviour enabling or disabling batch fetch; or enabling or disabling 2nd level cache and do not throw ClassCastException, but rather return null. 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