Need another Pre Delete Signal Type (feature)

[magneto]

the Pre delete signal is not all its cracked up to be ...

there should be another signal which is 'pre_prepare_for_delete'

This issuse is this

suppose i have 2 apps, all foreignkeyed to a user

####################
#Ap 1
class M1(models.Model):
  user = models.ForeignKey(User)
  very_transactional_stuff = models.CharFeld(max_length = 4)

def on_delete_user(sender, instance, *args, **kwargs):
     ASSIGN_TO_ROOT_ON_DELETE, created = User.object.get_or_create(username = 'UserDeleted')
     for m in M1.objects.filter(user = instance)
          m.user = ASSIGN_TO_ROOT_ON_DELETE
          m.save()
signals.pre_delete.connect(on_delete_user, sender = User)

####################
# Ap 2
class M1(models.Model):
  user = models.ForeignKey(User)
  very_transactional_stuff_two = models.CharFeld(max_length = 4)

def on_delete_user(sender, instance, *args, **kwargs):
     ASSIGN_TO_ROOT_ON_DELETE, created = User.object.get_or_create(username = 'UserDeleted')
     for m in M1.objects.filter(user = instance)
          m.user = ASSIGN_TO_ROOT_ON_DELETE
          m.save()

signals.pre_delete.connect(on_delete_user, sender = User)

Saddly this is what happens on a delete

• all the 'dependant' objects are obtained

# db.models.base.py Line 423
        # Find all the objects than need to be deleted.
        seen_objs = CollectedObjects()
        self._collect_sub_objects(seen_objs)

        # Actually delete the objects.
        delete_objects(seen_objs)

• pre_delete is called

# db.models.query Line 810
       # Pre-notify all instances to be deleted.
        for pk_val, instance in items:
            signals.pre_delete.send(sender=cls, instance=instance)

• uses the objects in the first step and DELETED them all, even after we have just 'reassinged' them (as the initial filter matched)

# db.models.query Lines 810 - 830

I propose another signal that is the 'pre_prepare_for_delete' that slips into

# db.models.base.py Line 423
        #first fire off the prepared signal
        signals.pre_prepare_for_delete.send(sender=self.__class__, instance=self)
		
        # Find all the objects than need to be deleted.
        seen_objs = CollectedObjects()
        self._collect_sub_objects(seen_objs)

        # Actually delete the objects.
        delete_objects(seen_objs)

Thoughts?

[(none)]

Milestone post-1.0 deleted

[Johannes Dollinger]

While the requested feature is different, the use-case is addressed by #7539.

[Johannes Dollinger]

Really a duplicate of #6108. (Related: #1007, #2288, #7539)

[cgieringer]

Related: #6870