#26042: types for GenericForeignKey object_pk?
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Reporter: brian | Owner: nobody
Type: Bug | Status: new
Component: Database layer (models, ORM) | Version: 1.9
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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Hello,
The documentation suggests that object_id associated with
GenericForeignKey should be a PositiveIntegerField. To be precise, the
documentation says: "For most models, this means a PositiveIntegerField."
but doesn't give any more details.
However, this will not work for pk that are not integer. So for the case
for django-guardian, where we want be more generic, we use a TextField.
I notice that object_id in django.contrib.admin.models LogEntry is a
TextField - although it doesn't use a GenericForeignKey.
The problem with this is when making table joins on Postgresql -
postgresql gets upset that the object_id is a string, and a different type
on the destination table.
e.g. simplified, we have a db model:
{{{
class UserObjectPermissionBase(models.Model):
content_type = models.ForeignKey(ContentType)
object_pk = models.CharField(_('object ID'), max_length=255)
content_object = GenericForeignKey(fk_field='object_pk')
}}}
We lookup certain objects from this table. For simplicity, lets assume
they *all* point to Group (django.contrib.auth) - i.e. content_type
points to the Group content type - as this is where the test case fails.
Also we use values, as we only are interested in the object_pk field.
{{{
user_obj_perms_queryset =
UserObjectPermissionBase.objects.filter(....).values('object_pk')
}}}
Then we want to lookup all groups that the results of this queryset point
to:
{{{
queryset.filter(Q(pk__in=user_obj_perms_queryset))
}}}
On sqlite and Mysql this works fine. On Postgresql it fails with a
Postgresql error:
{{{
======================================================================
ERROR: test_empty_perms_sequence
(guardian.testapp.tests.test_shortcuts.GetObjectsForUser)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/brian/tree/debian/upstream/django-
guardian/guardian/testapp/tests/test_shortcuts.py", line 474, in
test_empty_perms_sequence
set(objects),
File "/usr/lib/python2.7/dist-packages/django/db/models/query.py", line
162, in __iter__
self._fetch_all()
File "/usr/lib/python2.7/dist-packages/django/db/models/query.py", line
965, in _fetch_all
self._result_cache = list(self.iterator())
File "/usr/lib/python2.7/dist-packages/django/db/models/query.py", line
238, in iterator
results = compiler.execute_sql()
File "/usr/lib/python2.7/dist-
packages/django/db/models/sql/compiler.py", line 840, in execute_sql
cursor.execute(sql, params)
File "/usr/lib/python2.7/dist-packages/django/db/backends/utils.py",
line 64, in execute
return self.cursor.execute(sql, params)
File "/usr/lib/python2.7/dist-packages/django/db/utils.py", line 97, in
__exit__
six.reraise(dj_exc_type, dj_exc_value, traceback)
File "/usr/lib/python2.7/dist-packages/django/db/backends/utils.py",
line 64, in execute
return self.cursor.execute(sql, params)
ProgrammingError: operator does not exist: integer = character varying
LINE 1: ..."name" FROM "auth_group" WHERE ("auth_group"."id" IN (SELECT...
^
HINT: No operator matches the given name and argument type(s). You might
need to add explicit type casts.
}}}
The full SQL of the failing query in this case is:
{{{
SELECT "auth_group"."id", "auth_group"."name" FROM "auth_group" WHERE
("auth_group"."id" IN (SELECT U0."object_pk" FROM
"guardian_userobjectpermission" U0 INNER JOIN "auth_permission" U2 ON (
U0."permission_id" = U2."id" ) WHERE (U0."user_id" = 1 AND
U2."content_type_id" = 2)) OR "auth_group"."id" IN (SELECT U0."object_pk"
FROM "guardian_groupobjectpermission" U0 INNER JOIN "auth_group" U1 ON (
U0."group_id" = U1."id" ) INNER JOIN "testapp_customuser_groups" U2 ON (
U1."id" = U2."group_id" ) INNER JOIN "auth_permission" U4 ON (
U0."permission_id" = U4."id" ) WHERE (U2."customuser_id" = 1 AND
U4."content_type_id" = 2)))
}}}
Where I believe the problem is that "auth_group"."id" is integer and
U0."object_pk" is a string, and they can't be compared.
{{{
... WHERE ... "auth_group"."id" IN (SELECT U0."object_pk" FROM ...) ...
}}}
So is this a problem with our code? Maybe GenericForeignKey must have an
integer value, which excludes it from non-integer pks? Or is this a
problem with Django?
Would be interested in feedback.
Thanks
--
Ticket URL: <https://code.djangoproject.com/ticket/26042>
Django <https://code.djangoproject.com/>
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