django - OneToOneField and Deleting

Question

I have the following model:

from django.db import models
from django.contrib.auth.models import User


class Profile(models.Model):
    user = models.OneToOneField(User)
    # ...

    def __unicode__(self):
        return u'%s %s' % (self.user.first_name, self.user.last_name)

When using the Django admin to delete the user, the profile gets deleted as well, which is what I want. However, when using the Django admin to delete the profile, the user does not get deleted, which is not what I want. How can I make it so that deleting the profile will also delete the user?

Answer 1

Since Profile links to User, it is the dependent model in the relationship. Therefore when you delete a user, it deletes all dependent models. However when you delete a profile, since User does not depend on profile, it is not removed.

Unfortunately, according to on_delete Django docs, there is no on_delete rule which deletes the parent relations. In order to do that, you can overwrite the Profile's delete method:

class Profile(models.Model):
    # ...

    def delete(self, *args, **kwargs):
        self.user.delete()
        return super(self.__class__, self).delete(*args, **kwargs)

Then when doing:

Profile.objects.get(...).delete()

will also delete the profile's user. However the delete method will not be called when deleting profiles using querysets (which is what is called in Django Admin) since then Django uses SQL DELETE to delete objects in bulk:

Profile.objects.filter(...).delete()

In that case, as recommended by Django docs, you will have to use post_delete signal (docs).

from django.dispatch import receiver
from django.db.models.signals import post_delete

@receiver(post_delete, sender=Profile)
def post_delete_user(sender, instance, *args, **kwargs):
    if instance.user: # just in case user is not specified
        instance.user.delete()