CODEWITHSUNDEEP
pythondjango
Mathis
Mathis

Reputation: 41

Django: Adding many-to-many relations within post_save

I'm working on a Django 2.0 and I'm trying to create a simple Event app with auto opt-in functionality. I.e. Members with certain statuses are automatically signed up for the Event when it is created.

To do that, I used Django's post_save signal to create a queryset of the affected Members and add them to the Event's many-to-many field, participants.

@receiver(signal=post_save, sender='events.Event')
def auto_opt_in(sender, instance, created, **kwargs):
    # Only applies to new Events that are opt-out
    if created and instance.is_opt_out:
            from database.models import Member

            # Build queryset of affected members
            members = Member.objects.none()
            for status in instance.opt_out_member_statuses:
                members = members.union(Member.objects.filter(member_status=status))

            # Add members to Event
            instance.participants.add(*members)
            instance.save()

My problem now is that the Members are not actually added to the Event. If I put print(instance.participants.all()) after the last line, it outputs the correct result. However, the changes do not appear to be committed to the database. What am I missing? Are you not allowed to make changes to the instance? If so, what's the point?

Thanks

Upvotes: 2

Views: 201

Answers (1)

user2430441
user2430441

Reputation: 11

you need to do this:

from django.db import transaction

transaction.on_commit(lambda: instance.cou_group.add(instance.participants.add(*members))

why? i'm not sure

Upvotes: 1

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