How to save a record with null foreign key?

Question

Dear all,
Most articles show non-nullable foreign keys; but now I've got a problem with nullable foreign keys.
With this simple example: an employee has zero or one manager.
in manager object:
@OneToMany(cascade={CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH}, mappedBy="manager")
private Collection<Employee> employees;
in employee object:
@ManyToOne
@JoinColumn(name="manager_id")
private Manager manager;
when updating an employee record, i may use a selectOneMenu to pass a manager id of "0", I expect toplink to save a null manager_id in the employee record; but i tries to create a new manager object of id="0" (i.e. insert a new manager record instead)
the code i use to save an employee is like this:
em.getTransaction().begin();
em.merge(employee);
em.getTransaction().commit();
What's the correct way to save the employee record with a null manager_id column?
Could someone help?
Thanks a lot!
AK

Answer 1

But could you give me some pointers on how could I do
that from the web UI level?Got it. You want to select "nothing" and then set the object reference to that. I can't help you on JSF but how do you lookup the selected object behind the scenes? If you use entityManager.(Employee.class, 0) then you should get back null if there is no Employee with id=0.
--Shaun