Changing many-to-many using Admin Site never calls post_remove Signal

[Tobias Dacoir]

I have a many-to-many relationship which the Admin can change using the Admin Site. I use a ModelAdmin.filter_horizontal, but even with the default widget it's the same.

I registered a receiver when m2m_changed, however it always only calls: pre_clear, post_clear, pre_add, post_add, in that order.

Now for post_add I have code to execute, to create new objects in the database, however when a value is removed from this many-to-many field, I need to delete some objects. Since pre_remove is never called, I can't tell which value was removed and I'm unable to find out which objects to delete.

Is there a way to modify the Admin page to actually call remove / add on the Model? Or I need another way to find out which value was removed.

[Tobias Dacoir]

not very nice, and probably not pythonic (still learning) but now I added another two for loops to find old references and delete them:

    if action == "post_add":
        if isinstance(instance, Database):
            # then update pairs
            for a in instance.audioData():
                for q in instance.questions.all():
                    pair = AudioQuestionPair.objects.get_or_create(audioData=a, question=q, database=instance)
                    for choice in q.get_choices():
                        answer = Answer.objects.get_or_create(body=choice, audioQuestionPair=pair[0])
        # check for removed questions and delete pairs
        pairs = AudioQuestionPair.objects.filter(database=instance)
        toDelete = []
        for pair in pairs:
            if pair.question not in instance.questions.all():
                toDelete.append(pair)
        for item in toDelete:
            item.delete()