Hello all. Consider two entities: User and PhotoPushpin. Each user can create pushpin, but also user can have favorite photo pushpins. We have many-to-many association between User and PhotoPushpin (in favoritePhotoPushpins collection). It is unidirectional.

The question is: how to prevent a user to add the same photo pushpin to favorite twice? It means: how to make the composite key of both fields in association table to prevent two records to be absolutely equal? Or another way: how to add a key field to association table? Or maybe there is another way to solve this?

I've found something if to use annotations:



But I can't implement it because I use XML. I believe that there is the way to do it by XML. But how?

Hibernate version: 3.1

Mapping documents:

Association part of user.hbm.xml:



Name and version of the database you are using: MySql 4.0.26-nt

use <set> in place of <bag> and hibernate create a double primary key for you.

As for <set> I know it can prevent repetition. But can it be implemented with list? I consiter lists more preferable than sets. Or it was the only way?

if you generate the database with hibernate, you can use :


or direct add the constraint to the database self...

But I find this dangerous, you have to impose the unicity in your business (and use sets) and not let your database manage it!