Pete, Because when I do that I get transient instance problems: | 19:33:15,893 INFO [STDOUT] Hibernate: | insert | into | User_Calendar | (users_id, calendars_id) | values | (?, ?) | 19:33:15,895 ERROR [AbstractFlushingEventListener] Could not synchronize database state with session | org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: com.vivapop.calendar.entity.Calendar | at org.hibernate.engine.ForeignKeys.getEntityIdentifierIfNotUnsaved(ForeignKeys.java:219) | at org.hibernate.type.EntityType.getIdentifier(EntityType.java:397) | at org.hibernate.type.ManyToOneType.nullSafeSet(ManyToOneType.java:78) | at org.hibernate.persister.collection.AbstractCollectionPersister.writeElement(AbstractCollectionPersister.java:755) | at org.hibernate.persister.collection.AbstractCollectionPersister.recreate(AbstractCollectionPersister.java:1143) | at org.hibernate.action.CollectionRecreateAction.execute(CollectionRecreateAction.java:26) | at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:250) | ... | I searched hibernate forums about this and couldn't seem to find anything related ? View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4123265#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...