Django not cascading on delete

Question

I'm realizing more and more that I'm still a Django noob, I can't seem to figure out what's happening with my data model and why it's not cascading deletes. Here is my model.

class message(models.Model):
     msg_text = models.CharField(max_length = 9900)
     date_time = models.DateTimeField()
     is_read = models.BooleanField(default=False)


 class thread(models.Model):
     message = models.ForeignKey(message)
     subject = models.CharField(max_length=160)
     from_user = models.ForeignKey(User, related_name = 'from_user')
     to_user = models.ForeignKey(User, related_name = 'to_user')
     thread_id = models.CharField(max_length = 36)

def __unicode__(self):
    return self.subject

And then here is my delete function

def delete_message(request, thread_id):
     t = thread.objects.get(id=thread_id)
     thread.objects.filter(thread_id = t.thread_id).delete()

     return HttpResponseRedirect(reverse("inbox.views.index"))

So every thread has messages attached to it, and all the threads that contain related messages (ie replies) are all related with a thread id which is a randomly generated string. So when I delete I get the initial thread id (django auto-generated id) and then use it to grab the unique thread id and delete all entries that contain that thread ID. However when I delete the thread it is not auto-cascading and deleting the related message objects.

The weird thing is that it worked before, but then stopped working, I'm not too sure why. Any ideas?

Answer 1

In Django version 1.3 there is a on_delete parameter which determinates "ondelete" action, for example:

def get_sentinel_user():
    return User.objects.get_or_create(username='deleted')[0]

class MyModel(models.Model):
    user = models.ForeignKey(User, on_delete=models.SET(get_sentinel_user))

So maybe try:

class thread(models.Model):
     message = models.ForeignKey(message, on_delete=models.CASCADE)
     ...

source http://docs.djangoproject.com/en/1.3/ref/models/fields/

Answer 2

That's not how cascading delete works. Since thread has a foreign key to message, if you delete a message, the cascading effect is to delete all associated threads. See the documentation for more information and examples:

• Deleting objects

You could call delete on the associated message if that's what you want.