For that I get: javax.ejb.EJBException: javax.persistence.PersistenceException: org.hibernate.PersistentObjectException: detached entity passed to persist: entity.Test2 on the line that reads: entityManager.persist(t1); I guess that this is because the Test2 objects are being re-persisted, so I modified it to read: Test1 t1=new Test1(); ArrayList<Test2> a=new ArrayList<Test2>(); Test2 t2=new Test2(); t2.setField(1); entityManager.persist(t2); a.add(t2); t2=new Test2(); t2.setField(2); entityManager.persist(t2); a.add(t2); // t1.setTest2s(a); t1.setField(1); entityManager.persist(t1); t1.setTest2s(a); entityManager.merge(t1); the only issue being that the results are as in the initial case: no foreign keys I failed to mention it previously, but as to my ManyToMany relationships--the join table is created, and correctly, but there are never any rows inserted, even though either side has the correct data View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3957028#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...