M2M querysets not being invalidated on instance deletion

[tumb1er]

We have a model with a non-autoincremental primary key, which has an m2m relation.

After deleting and creating an instance with same primary keys, we are getting stale m2m cache.
This is mostly because of Django not sending m2m_changed on instance deletion (see https://code.djangoproject.com/ticket/17688).

I'll add a PR with a failing test later, but have no good decision of fixing this on the cacheops side. Also, the bug was very difficult to catch, lots of conditions must be satisfied, so I'd like to propose to add a workaround for Django on the cacheops side.

class Profile(Model):
   user = OneToOneField(User, CASCADE, primary_key=True)
   roles = ManyToManyField(Role, blank=True)

user = User.objects.create()
profile = Profile.objects.create(user=user)
role = Role.objects.create()

profile.roles.set([role])

assert len(list(profile.roles.all())) == 1

profile.delete()  # Here m2m relation is not invalidated

profile = Profile.objects.create(user=user)

assert len(list(profile.roles.all())) == 0  # Assertion fails

# Workaround

@receiver(pre_delete, sender=Profile)
def invalidate_m2m_after_delete(sender, instance, **kwargs):
    invalidate_dict(Profile.roles.through, {'profile_id': instance.pk})

[Suor]

Ok, waiting for a test.

[tumb1er]

Failing test here #408

I see multiple ways:

1. Catch pre_delete and traverse all m2m relations with calling "invalidate_dict" as in example workaround
2. Add m2m-related queries to "profile" conj (now it's on "through" model and on "role" side - see below)
3. Wait till Django issue will be fixed :(

1629124268.381713 [0 lua] "sadd" "schemes:profiles_role" ""
1629124268.381742 [0 lua] "sadd" "conj:profiles_role:" "q:d7b4c0ab39dd2d595b2dc6f70463e1a8"
1629124268.381784 [0 lua] "ttl" "conj:profiles_role:"
1629124268.381807 [0 lua] "expire" "conj:profiles_role:" "172810"
1629124268.381835 [0 lua] "sadd" "schemes:profiles_profile_roles" "profile_id"
1629124268.381871 [0 lua] "sadd" "conj:profiles_profile_roles:profile_id=17" "q:d7b4c0ab39dd2d595b2dc6f70463e1a8"
1629124268.381910 [0 lua] "ttl" "conj:profiles_profile_roles:profile_id=17"
1629124268.381937 [0 lua] "expire" "conj:profiles_profile_roles:profile_id=17" "172810"

[Suor]

So, it's Django issue? Did you file a ticket there?

[tumb1er]

It's a ten years old ticket without any movement on last 5 years.
https://code.djangoproject.com/ticket/17688

So I think there will be no fix at Django side

[Suor]

I'll take a look.

[Suor]

Unfortunately there is no quick fix for this.