Django signal m2m_changed not triggered

Question

I recently started to use signals in my Django project (v. 1.3) and they all work fine except that I just can't figure out why the m2m_changed signal never gets triggered on my model. The Section instance is edited by adding/deleting PageChild inline instances on an django admin form.

I tried to register the callback function either way as described in the documentation, but don't get any result.

Excerpt from my models.py

from django.db import models
from django.db.models.signals import m2m_changed


class Section(models.Model):
    name = models.CharField(unique = True, max_length = 100)
    pages = models.ManyToManyField(Page, through = 'PageChild')

class PageChild(models.Model):
    section = models.ForeignKey(Section)
    page = models.ForeignKey(Page, limit_choices_to = Q(is_template = False, is_background = False))


@receiver(m2m_changed, sender = Section.pages.through)
def m2m(sender, **kwargs):
    print "m2m changed!"

m2m_changed.connect(m2m, sender = Section.pages.through, dispatch_uid = 'foo', weak = False)

Am I missing something obvious?

Where you able to figure this out? Looking for the same answer. — Simon Klee, Aug 25 '11 at 11:24
Sometimes when I copy and paste code from another signal receiver I forget to update the function name and only one of them runs. — freb, Feb 11 '15 at 23:14

score 12 · Answer 1 · answered Jan 19 '12 at 18:40

12

This is an open bug: https://code.djangoproject.com/ticket/16073

I wasted hours on it this week.

answered Jan 19 '12 at 18:40

jblaine

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I can't believe this is still an open issue. headaches included. – stealthwang Dec 02 '14 at 04:43
Is this still an open issue? Can't believe it – Stefano Munarini Aug 03 '21 at 15:15
No, it's not an open issue anymore. My reply above was from 2012. – jblaine Aug 03 '21 at 21:12

score 3 · Answer 2 · edited Feb 08 '13 at 09:26

3

You are connecting it twice, once with m2m_changed.connect and the other time with receiver decorator.

edited Feb 08 '13 at 09:26

mipe34

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answered Feb 08 '13 at 09:07

vijay shanker

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score 2 · Answer 3 · answered Sep 01 '11 at 14:27

2

Not sure if it will help, but the following is working for me:

class Flow(models.Model):
    datalist = models.ManyToManyField(Data)

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

def handle_flow(sender, instance, *args, **kwargs):
    logger.debug("Signal catched !")

m2m_changed.connect(handle_flow, sender=Flow.datalist.through)

answered Sep 01 '11 at 14:27

Stéphane

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This one is different from what the user asked. What the original question was referring to was a scenario where he was using an explicit Model "PageChild" to specify the relation here. – kingpin Mar 26 '14 at 09:50
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Even without using the explicit 'through' argument this signal will fail if you use inline admin forms like StackedInline. – stealthwang Dec 02 '14 at 14:57

score 0 · Answer 4 · answered Jun 24 '11 at 06:24

0

I'm not sure if this will help, but are you sure that you should use Sender.pages.through for this special case? perhaps if you tried @reciever(m2m_changed, sender=PageChild)

Note: if you have @reciever, you do not need m2_changed.connect(...) as @reciever already performs the connect operation.

answered Jun 24 '11 at 06:24

Thomas

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I tried it with PageChild too, but didn't change anything. Problem is that neither of two ways to register the callback works, that's why I included both. :/ – user543424 Jun 24 '11 at 06:51

Django signal m2m_changed not triggered

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