Question

I’ve got two tables A and B with simple PK’s.

@Entity
public class A { 
    @Id
    public int idA;
}

@Entity
public class B { 
    @Id
    public int idB;
}

I want to map a new association class AB that simply stores the relations between A and B, with composite PK idA+idB. AB doesn’t have any extra columns, just the relation between idA and idB.

Is it possible to map AB using a single class? I want to avoid having to create a new ABId class just to use it as @IdClass or @EmbeddedId in AB, and I don’t want to map this with a @ManyToMany association on A or B.

Answer 1

Why do you want to map such a join table? Just use a ManyToMany association between A and B. This join table will then be handled automatically when you’ll add/remove a B to/from the list of Bs contained in A.

See http://docs.jboss.org/hibernate/core/3.6/reference/en-US/html_single/#d0e11402

If you really want to do that, then just map the two IDs with the @Id notation. The primary class will be the entity class itself (which must be serializable), as explained in the hibernate reference documentation. Note that this is Hibernate-specific.