Hi All! I have a quite strange data model, but it has it explanation. Lets say we have the following tables in my db: | | ----------- | | A | | ----------- | | Aid (pk)| | | | | ----------- | | | ----------- | | B | | ----------- | | Bid (pk)| | | Aid (fk)| | | | | ----------- | | | ----------- | | C | | ----------- | | Aid (pk)| | | Bid (fk)| | | | | ----------- | There is a unique constraint on the tuple (Aid, Bid) | | A textual explanation of the model: A is the master table. It has more info than the columns I described. But the most important one is the primary key Aid. B is another table. Items in B references A, i.e. there are many B items on one A item (many-to-one). C is a table that will point out one row in B from A. So there is a one-to-one relationship between A and B that is stored in table C. The problem here is that we have a kind of circular reference. Is it possible to model this in EJB3 with annotation. I have tried a lot, but nothing works. I often get a NPE for OneToOne on line 135. The classesre defined as follows: | | public class A { | | @Id | @GeneratedValue(strategy = GenerationType.IDENTITY) | @Column(name = "Aid") | private Integer id; | | @OneToMany(cascade = CascadeType.ALL, mappedBy = "A", fetch = FetchType.LAZY) | private List<B> Bs = new ArrayList<B>(); | | | @OneToOne | @PrimaryKeyJoinColumn | private C c = null; | | ... | } | | | | public class B { | | @Id | @GeneratedValue(strategy = GenerationType.IDENTITY) | @Column(name = "Bid") | private Integer Bid; | | @ManyToOne | @JoinColumn(name = "Aid", nullable = false) | private A a; | | ... | } | | | public class C { | | @Id | @Column(name = "Aid") | private Integer id; | | @OneToOne | @JoinColumn(name = "Aid", nullable=false) | private A a; | | @OneToOne | @PrimaryKeyJoinColumn | private B b; | | ... | } | | So, it is a problem doing this way. Does anyone know how to get it to work. I know the datamodel is a bit tricky - the explanation I have is that we want all references to A be in the same direction. Environment: JBoss 4.0.5.GA JBoss EJB3 RC9 Patch JBoss WS 1.2.0GA SP1 Database MySQL 5, no InnoDB I would really appreciate if someone can help me Best Regards Oskar View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4033045#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...