Hi I have a question about association classes.

As an example I have a class User and Group. Users can be members of many groups and Groups can have many Users. I am using an association class called UserGroup, which basically contains 2 many-to-one associations, linking a User to a Group. From the documentation this seems to be the
preferred way of modelling the many-to-many relation between User and Group. Is this assumption valid?

If so then my question is this. When I come to delete a User, I need to delete
the UserGroup entries where that user is part of. Is there an automatic way of doing this (perhaps with cascade="delete" ? ) or in my User.remove logic do I have to explicitly delete UserGroup entries prior to deleting the user?

Thanks,

Hani

1. Yes it is valied. We've barely seen a true many-to-many association in rela life applications, you usualiiy have to add some proeprties tot he association sooner or later.
2. cascade="delete" works

If you've some bucks, buy Hibernate In action, it's well explained.

Hi Emmanuel, thanks for the reply. I have bought the ebook (missing the appendices though, since I forgot to download them when they came out).

But after re-reading Chapter 6 I am still stuck. I have no problems associating Users to Groups. The problem that I have is when I attempt to delete a User or a Group that is linked in a UserGroup association. I get
DataIntegrityViolationException which sort of makes sense. What I wanted
to know if there was a way to tell hibernate that when I delete a User I also want all UserGroup objects that reference that User to be deleted. cascade="delete" does not work, since I think it refers to the other direction.
Note that User class has no reference to UserGroup.

A solution to my problem would be to delete the UserGroup entries prior to
deleting the User. But this would complicate my code ( since plugins are
involved etc.. ). But perhaps it is the only way to do it, I just wanted to make
sure of that before I start complicating the code :)

Regards,
Hani

You should explicit this association and mark the user.getUserGroup() as cascade="delete", otherwise, Hibernate has no (good) way to know the link.