Detached entity cannot be merged via cascade merge in JBoss EAP 6

Solution Verified - Updated -


  • Migrating Hibernate 3 application to Hibernate 4
  • EntityA has two CascadeType.MERGE associations to EntityB: relatedB1 and relatedB2
  • An instance of EntityB is instantiated, persisted, detached then associated with EntityA via relatedB1
  • The persisted instance of EntityB is loaded by a query and associated with EntityA via relatedB2
  • When EntityA is merged to the data store, an exception like the following is raised:
java.lang.IllegalStateException: Error occurred while storing entity [test.EntityB@20]. An entity copy [test.EntityB#1] was already assigned to a different entity [test.EntityB@20].
    at org.hibernate.event.internal.EventCache.put(
    at org.hibernate.event.internal.DefaultMergeEventListener.entityIsDetached(
    at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(
    at org.hibernate.internal.SessionImpl.merge(
    at org.hibernate.ejb.AbstractEntityManagerImpl.merge(


  • Red Hat JBoss Enterprise Application Platform (EAP) 6
  • Hibernate 4.1.3 and later

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