[hibernate-users] One to one bi-directional mappings

Dear List, Perhaps you can help? I've done a number of Hibernate mappings before now, but something has left me puzzled. If I have objects A and B, where A has a one to one bi-directional relationship with B, I define them as follows: public class A { private B b; ... @OneToOne(cascade=CascadeType.ALL) @JoinColumn(name="FK_b", nullable=false) public B getB() { return b; } } public class B { private A a; @OneToOne(mappedBy="b") public A getA() { return a; } } This works perfectly. However, what if I want A to have multiple instances of B, i.e.: public class A { protected B b1, b2; @OneToOne(cascade=CascadeType.ALL) @JoinColumn(name="FK_b1", nullable=false) public B getB1() { return b1; } @OneToOne(cascade=CascadeType.ALL) @JoinColumn(name="FK_b2", nullable=false) public B getB2() { return b2; } } The object B still only has one parent (A), so how is this defined? Any thoughts are most welcome. John