Content Type framework does not trigger Cascade delete

[JoseTomasTocino]

I've posted this question in StackOverflow (​http://stackoverflow.com/questions/23528296/djangos-content-type-framework-does-not-trigger-cascade-delete) and given it looks like a bug, I've decided to post it here.

Suppose the following models:

class DeltaCheck(models.Model):
    logs = generic.GenericRelation('Log')
    title = models.CharField(max_length=50)
    owner = models.ForeignKey(User)

class Log(models.Model):
    title = models.CharField(max_length=50)

    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    content_object = generic.GenericForeignKey('content_type', 'object_id')

If I create a DeltaCheck and a couple of Logs and then delete the DeltaCheck, the Logs are deleted as well:

In [7]: Log.objects.count()
Out[7]: 10

In [8]: DeltaCheck.objects.get().delete()

In [9]: Log.objects.count()
Out[9]: 0

BUT if I delete the User (the field owner), the DeltaCheck gets deleted BUT not the Logs, look:

In [14]: Log.objects.count()
Out[14]: 10

In [15]: DeltaCheck.objects.get().owner.delete()

In [16]: DeltaCheck.objects.all()
Out[16]: []

In [17]: Log.objects.count()
Out[17]: 10

Is that proper behavior? I don't think so.

[JoseTomasTocino]

Wait... If I define an empty signal receiver, it works! (????) I've just added:

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

@receiver(pre_delete)
def pre_delete_receiver(**kwargs):
    pass

And now the deletion is performed...

[chk]

I'm able to reproduce the same issue with a similar database schema.

• django 1.6.1
• postgresql 9.1

As a workaround I've defined a pre_signal (but NOT empty as Jose says):

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

@receiver(pre_delete, sender=User)
def pre_delete_receiver(sender, instance, **kwargs):
    ## CODE TO DELETE RELATED OBJECTS
    for delta in instance.deltachecks.all():
        delta.logs.all().delete()

[Baptiste Mispelon]

Hi,

I can also reproduce this issue (and indeed, having an empty signal fixes the issue).

For reference, cascade deletion of generic foreign keys is documented and only works if you have a reverse GenericRelation [1] (last two paragraphs).

The key to this issue probably lies in the fast_delete method [2] (note for example the line 126 that explains why things behave differently if there is a signal listening or not).

Thanks.

[1] ​https://docs.djangoproject.com/en/1.6/ref/contrib/contenttypes/#django.contrib.contenttypes.generic.GenericRelation
[2] ​https://github.com/django/django/blob/master/django/db/models/deletion.py#L110

[Anssi Kääriäinen]

This is likely a duplicate of #22998 which has a patch. I am not going to close this yet as duplicate as I haven't verified that the fix in #22998 also fixes this issue.

[Nick Sandford]

I can confirm that #22998 fixes the issue, closing as fixed.