I have the following models (simplified example): class Book(models.Model): users = models.ManyToManyField(User, through=Permission)
class Permission(models.Model): user = models.ForeignKey(User) role = models.ForeignKey(Group) active = models.BooleanField() book = models.ForeignKey(Book) What I need is that for a Book instance there cannot be more than one User of with the same Role and Active. So this is allowed: Alice, Admin, False (not active), BookA Dick, Admin, True (active), BookA Chris, Editor, False (not active), BookA Matt, Editor, False (not active), BookA But this is not allowed: Alice, Admin, True (active), BookA Dick, Admin, True (active), BookA Now this cannot be done using unique_together, because it only counts when active is True. I've tried to write a custom clean/ validate_unique method (like how I have done here: http://stackoverflow.com/questions/3052427/validation-on-manytomanyfield-before-save-in-models-py/3266169#3266169). But it seems that when you save a Book and it runs the validation on each Permission, the already validated Permission instances aren't saved until they've all been validated. This makes sense, because you don't want them to be saved in case something doesn't validate. Could anyone tell me if there is a way to perform the validation described above? P.S. I could imagine using the savepoint feature (http:// docs.djangoproject.com/en/1.2/topics/db/transactions/), but I only really want to consider that as a last resort. Note! I first posted this question on StackOverflow. I received a response but the answer wouldn't work for me. Please have a look at the response to avoid repeating the answer: http://stackoverflow.com/questions/3759687/ -- You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-us...@googlegroups.com. To unsubscribe from this group, send email to django-users+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/django-users?hl=en.
