Clear nullable foreign keys on delete

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
from django.db import models

class Model(models.Model):
    """
    Intermediate model base class.
    """
    class Meta:
        abstract = True

    def delete(self, *args, **kwargs):
        self.clear_nullable_related()
        super(Model, self).delete(*args, **kwargs)

    def clear_nullable_related(self):
        """
        Recursively clears any nullable foreign key fields on related objects.
        Django is hard-wired for cascading deletes, which is very dangerous for
        us. This simulates ON DELETE SET NULL behavior manually.
        """
        for related in self._meta.get_all_related_objects():
            accessor = related.get_accessor_name()
            related_set = getattr(self, accessor)

            if related.field.null:
                related_set.clear()
            else:
                for related_object in related_set.all():
                    related_object.clear_nullable_related()

More like this

  1. PostgreSQL ON DELETE CASCADE by mjt 3 years, 6 months ago
  2. Generate thumbnails on save by peterw 4 years, 6 months ago
  3. Allow filtering and ordering by counts of related query results by exogen 6 years, 1 month ago
  4. FilterSpec for ForeignKeys to auth.User with HTML input tag for ModelAdmin.list_filter by loic 2 years ago
  5. Foreign Key list_filter wthout custom FilterSpec by haileris23 3 years, 3 months ago

Comments

jdunck (on December 11, 2008):

psagers, I'm not on 1.0 yet, but reading the code in model.delete() and delete_objects(), it sure looks to me like Django goes out of its way to avoid deleting nullable foreign keys on model_instance.delete.

Is this an actual problem you're seeing? Are you doing Model.delete or QuerySet.delete?

In any case, it sounds like it might be a bug. Did you file a ticket?

#

peterbe (on June 8, 2010):

@jdunck this is still a problem. Even in Django 1.2.1

#

skyjur (on July 28, 2010):

I've modified clear_nullable_related() because I was getting exceptions in some cases. Here is my modified code:

from django.core.exceptions import ObjectDoesNotExist

def clear_nullable_related(self):
    """
    Recursively clears any nullable foreign key fields on related      objects.
    Django is hard-wired for cascading deletes, which is very dangerous for
    us. This simulates ON DELETE SET NULL behavior manually.
    """
    for related in self._meta.get_all_related_objects():
        accessor = related.get_accessor_name()
        try:
            related_set = getattr(self, accessor)
        except ObjectDoesNotExist:
            continue

        if related.field.null:
            related_set.clear()
        elif related.field.rel.multiple:
            for related_object in related_set.all():
                related_object.clear_nullable_related()

#

guettli (on March 14, 2012):

Django 1.3 has support for "ON DELETE": ForeignKey.on_delete

#

(Forgotten your password?)