On 16 Feb 2004 16:02, hengels wrote:

>what about using the primary key and fall back to object identity if a
>pk is not assigned?

This breaks collections because it changes the object's hashcode once
you save it.  So you would get:

UserManager u = session.load(UserManager.class, id);

User newUser = new User("newUsername1");
u.getUserSet().add(newUser); // adds a new Entity with id = null or id = 0
session.save(newUser);
session.flush();             // The id is now assigned to the newUser object
if (!u.getUserSet().contains(newUser)) System.err.print("OOPS!");

This *will* print "OOPS!" because newUser's hashcode changed when you
saved it, so the userSet can no longer find it.

See this forum thread http://forum.hibernate.org/viewtopic.php?t=928172
for an exhaustive discussion of this problem.