Opened 6 years ago

Closed 15 months ago

Last modified 15 months ago

#14196 closed New feature (fixed)

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

Reported by: mark0978 Owned by:
Component: Database layer (models, ORM) Version: master
Severity: Normal Keywords:
Cc: Triage Stage: Accepted
Has patch: no Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no


def avatar_url(user, size=80):
    if not isinstance(user, User):
            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]
        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.

Change History (11)

comment:1 Changed 6 years ago by niall

  • Component changed from Uncategorized to Database layer (models, ORM)
  • Needs documentation unset
  • Needs tests unset
  • Patch needs improvement unset
  • Triage Stage changed from Unreviewed to Accepted
  • Version changed from 1.2 to SVN

comment:2 Changed 5 years ago by graham_king

  • Severity set to Normal
  • Type set to New feature

comment:3 Changed 5 years ago by aaugustin

  • UI/UX unset

Change UI/UX from NULL to False.

comment:4 Changed 5 years ago by aaugustin

  • Easy pickings unset

Change Easy pickings from NULL to False.

comment:5 Changed 15 months ago by zedr

  • Owner changed from nobody to zedr
  • Status changed from new to assigned

Assigning to myself for work.

comment:6 Changed 15 months ago by zedr

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?

comment:7 Changed 15 months ago by zedr

  • Owner zedr deleted
  • Status changed from assigned to new

comment:8 Changed 15 months ago by timgraham

  • Resolution set to fixed
  • Status changed from new to closed

comment:9 Changed 15 months ago by carljm

Thanks for investigating!

comment:10 Changed 15 months ago by mark0978

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.

comment:11 Changed 15 months ago by aaugustin

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.

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