Django: m2m_changed not fired when end of relation

Question

NOTICE: due to production environment constraints, I must stick to django-1.4 for the moment.

I've just made a test to see whether I can hook onto an event when ManyToMany changes.

I have a Group model that holds several Item objects. Whenever the items change in any group, I want to do something with concerned Group` instances.

from django.db import models
    from django.db.models.signals import m2m_changed, post_delete, pre_delete

class Item(models.Model):
    name = models.CharField(max_length=32)

    def __str__(self):
        return self.name

class Group(models.Model):
    name = models.CharField(max_length=32)
    items = models.ManyToManyField(to=Item)    

def items_changed(signal, sender, action, instance, reverse, model, pk_set, using, **kwargs):
    print str(signal)
    print action, instance, reverse, pk_set

m2m_changed.connect(items_changed, sender=Group.items.through)

If I change the items list on a Group instance, I the m2m_changed event is obviously fired.

>>> from sandbox.core.models import Group, Item
>>> item, created = Item.objects.get_or_create(name='f')
>>> g = Group.objects.get(pk=1)
>>> g.items.add(item)
pre_add Group object False set([5])
post_add Group object False set([5])
>>> g.items.remove(item)
pre_remove Group object False set([5])
post_remove Group object False set([5])

Now, when I remove the Item end of the relation, nothing happens, however, the relation table entry is correctly deleted.

>>> item.delete()

I tried connecting to the delete signal of the m2m through table, but apparently, signals are not fired for the automatic relation tables.

Connected like this in my models.py module:

def group_items_pre_delete(signal, sender, instance, using, **kwargs):
    print 'pre_delete', instance

def group_items_post_delete(signal, sender, instance, using, **kwargs):
    print 'post_delete', instance

pre_delete.connect(group_items_pre_delete, sender=Group.items.through)
post_delete.connect(group_items_post_delete, sender=Group.items.through)

The solution I have for now is to check manually for changes. The models are exposed through a REST API, so I can do this when an update request ends (but I would have liked it to be automated through the signals).

Are those "missing" signals fired in any newer version of Django?

Answer 1

This is a bug, not fixed yet: https://code.djangoproject.com/ticket/17688