Hibernate: org.hibernate.NonUniqueObjectException: another object with the same identifier value was already associated with the session

Question

I wonder why this exception occurs, although it is guaranteed by the Hibernate get / query methods to retrieve objects that are already available in a Hibernate session if these objects are required again:

org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: [xyzMyObject#130062] at org.hibernate.engine.StatefulPersistenceContext.checkUniqueness(StatefulPersistenceContext.java:638) at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.performUpdate(DefaultSaveOrUpdateEventListener.java:305) at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsDetached(DefaultSaveOrUpdateEventListener.java:246) at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:112) at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:93) at org.hibernate.impl.SessionImpl.fireSaveOrUpdate(SessionImpl.java:685) at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:677) at org.hibernate.engine.CascadingAction$5.cascade(CascadingAction.java:252) at org.hibernate.engine.Cascade.cascadeToOne(Cascade.java:392) at org.hibernate.engine.Cascade.cascadeAssociation(Cascade.java:335) at org.hibernate.engine.Cascade.cascadeProperty(Cascade.java:204) at org.hibernate.engine.Cascade.cascadeCollectionElements(Cascade.java:425) at org.hibernate.engine.Cascade.cascadeCollection(Cascade.java:362) at org.hibernate.engine.Cascade.cascadeAssociation(Cascade.java:338) at org.hibernate.engine.Cascade.cascadeProperty(Cascade.java:204) at org.hibernate.engine.Cascade.cascade(Cascade.java:161) at org.hibernate.engine.Cascade.cascade(Cascade.java:127) at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.cascadeOnUpdate(DefaultSaveOrUpdateEventListener.java:376) at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.performUpdate(DefaultSaveOrUpdateEventListener.java:350) at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsDetached(DefaultSaveOrUpdateEventListener.java:246) at org.hibernate.event.def.DefaultUpdateEventListener.performSaveOrUpdate(DefaultUpdateEventListener.java:57) at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:93) at org.hibernate.impl.SessionImpl.fireUpdate(SessionImpl.java:742) at org.hibernate.impl.SessionImpl.update(SessionImpl.java:730) at org.hibernate.impl.SessionImpl.update(SessionImpl.java:722) 

Answer 1

After some debugging, it turned out that I did not stop the cascading update distribution inside the self-named model:

type1 → type2 → type3 → collection (type1)

So, all that had to be done was to stop cascading with cascade="none" :

 <set name="type1collection" ... cascade="none"> ... </set> 

This means that another object with the same identifier value was already associated with a session that was hidden inside self-naming children. Additional updating of these children is not required, therefore cascading is not correct.