Objects that come from something_set, should have their parent object filled in

[Mark Jones]

def avatar_url(user, size=80):
    if not isinstance(user, User):
        try:
            user = User.objects.get(username=user)
        except User.DoesNotExist:
            return AVATAR_DEFAULT_URL
    avatars = user.avatar_set.order_by('-date_uploaded')
    primary = avatars.filter(primary=True)
    if primary.count() > 0:
        avatar = primary[0]
    elif avatars.count() > 0:
        avatar = avatars[0]
    else:
        avatar = None
    if avatar is not None:
        avatar.user = user # prevent an extra lookup because the avatar doesn't know he came from user.avatar_set

If I don't put in the last line in that sample, accessing avatar.user will again query the database to get the "parent" object. It seems to me that when you do user.avatar_set.all(), the user in the avatar object would get set before the object is returned, but that isn't the case, instead it loads another user object from the db and stuffs it into the avatar object.

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Aymeric Augustin]

Change Easy pickings from NULL to False.

[Rigel Di Scala]

Assigning to myself for work.

[Rigel Di Scala]

I cannot reproduce this using the following test:

    def test_prepopulated_parent_of_a_set(self):
        my_user = User.objects.create(username="MyUser")
        LogEntry.objects.create(user=my_user, action_flag=0)

        user_logs = my_user.logentry_set.all()
        first_log = user_logs[0]
        with self.assertNumQueries(0):
            log_user = first_log.user
            self.assertEquals(my_user.username, log_user.username)

This test passes, meaning no additional queries were executed when attempting to lookup the parent user. Maybe I'm missing something obvious?

[Carl Meyer]

Thanks for investigating!

[Mark Jones]

I'm betting over the course of the last 5 years this got fixed. Might be a good idea to add the test code to prevent regression though.

[Aymeric Augustin]

known_related_objects.tests.ExistingRelatedInstancesTests.test_foreign_key tests this.

I couldn't find easily when it was introduced because the modeltests/regressiontests merge breaks git log.