id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
24738	"No ""m2m_changed"" signal sent when deleting related objects"	No-0n3	nobody	"Hi,

I looked at #6707 and it isn't a problem about M2M in admin I'm talking about. Installed the master branch from github and tested. If the solution in #6707 solved my problem but it didn't.

I'm trying to delete all objects from the database that doesn't have any relation by signaling that the relationship has been changed with the ""m2m_changed"" signal.

If I delete a model through the shell with ""<object>.delete()"", then no ""m2m_changed"" signal is sent that any relations has been changed in any way.

Here is my test:
{{{
Python 2.7.9 (default, Dec 12 2014, 07:23:35) 
[GCC 4.9.2] on linux2
Type ""help"", ""copyright"", ""credits"" or ""license"" for more information.
(InteractiveConsole)
>>> from blacklist.models import Blacklist, Record
>>> l = Blacklist.objects.create(name=""test"")
>>> r = Record.objects.create(ip=""127.0.0.2"")
>>> r.blacklists.add(l)
{'reverse': False, 'signal': <django.db.models.signals.ModelSignal object at 0x7606ad30>, 'instance': <Record: 127.0.0.2>, 'pk_set': set([10L]), 'using': 'default', 'model': <class 'blacklist.models.Blacklist'>, 'action': u'pre_add'}
{'reverse': False, 'signal': <django.db.models.signals.ModelSignal object at 0x7606ad30>, 'instance': <Record: 127.0.0.2>, 'pk_set': set([10L]), 'using': 'default', 'model': <class 'blacklist.models.Blacklist'>, 'action': u'post_add'}
>>> Record.objects.all() 
[<Record: 127.0.0.1>, <Record: 127.0.0.2>]
>>> Record.objects.all()[0].blacklists.add(l)
{'reverse': False, 'signal': <django.db.models.signals.ModelSignal object at 0x7606ad30>, 'instance': <Record: 127.0.0.1>, 'pk_set': set([10L]), 'using': 'default', 'model': <class 'blacklist.models.Blacklist'>, 'action': u'pre_add'}
{'reverse': False, 'signal': <django.db.models.signals.ModelSignal object at 0x7606ad30>, 'instance': <Record: 127.0.0.1>, 'pk_set': set([10L]), 'using': 'default', 'model': <class 'blacklist.models.Blacklist'>, 'action': u'post_add'}
>>> Record.objects.all()
[<Record: 127.0.0.1>, <Record: 127.0.0.2>]
>>> Blacklist.objects.all()
[<Blacklist: test>]
>>> Blacklist.objects.all()[0].record_set.all()
[<Record: 127.0.0.1>, <Record: 127.0.0.2>]
>>> l = Blacklist.objects.all()[0]
>>> l
<Blacklist: test>
>>> l.delete()
>>> Record.objects.all()
[<Record: 127.0.0.1>, <Record: 127.0.0.2>]
>>> Record.objects.all()[0].blacklists.all()
[]
>>>
}}}

The signal receiver function:
{{{
@receiver(m2m_changed, sender=Record.blacklists.through)
def blacklists_changed(sender, **kwargs):
    print ""%s"" % kwargs # Only to see if any data was sent and to see if an m2m_changed signal was received.

    if kwargs['action'] == ""post_clear"":
        if kwargs['reverse']:
            Record.objects.annotate(count=Count('blacklists')).exclude(count__gt=0).delete()
}}}

No signal is sent at deletion of a related object when the relation was broken by deleting the object. Sorry but it isn't a duplication. Because I don't get any output that the signal function has run as when I ran the ""add""-relation function and the related objects are still there without any relation to a object. If I uncomment the second function that catch a ""pre_delete"" and explicitly call ""clear()"" on the M2M-field I receive a ""m2m_changed"" signal and all records without a related object are deleted. According to docs ""m2m_changed"" was a signal that is sent when the relationship between objects are changed, which happens when the object is deleted.

Entire code:
{{{
from django.db import models
from django.db.models.signals import m2m_changed, pre_delete
from django.dispatch import receiver
from django.db.models import Count


# Models
class Type(models.Model):
    name = models.CharField(max_length=200)

    def __unicode__(self):
        return unicode(self.name)


class Blacklist(models.Model):
    source = models.URLField()
    name = models.CharField(max_length=200)
    date_added = models.DateField(auto_now_add=True)
    last_update = models.DateField(auto_now=True)
    types = models.ManyToManyField(Type)

    def __unicode__(self):
        return unicode(self.name)


class Record(models.Model):
    blacklists = models.ManyToManyField(Blacklist)
    ip = models.GenericIPAddressField(protocol='IPv4', unique=True)

    def __unicode__(self):
        return unicode(self.ip)


# Signal actions
@receiver(m2m_changed, sender=Record.blacklists.through)
def blacklists_changed(sender, **kwargs):
    print ""%s"" % kwargs

    if kwargs['action'] == ""post_clear"":
        if kwargs['reverse']:
            Record.objects.annotate(count=Count('blacklists')).exclude(count__gt=0).delete()


#@receiver(pre_delete, sender=Blacklist)
#def blacklist_deleted(sender, **kwargs):
#    kwargs['instance'].record_set.clear()
}}}

BR / Isaac"	Bug	closed	Database layer (models, ORM)	dev	Normal	duplicate		No-0n3	Unreviewed	0	0	0	0	0	0