#25747: djorm-ext-filtered-contenttypes impossible on Django 1.9
-------------------------------------+-------------------------------------
Reporter: mpasternak | Owner: nobody
Type: Uncategorized | Status: new
Component: Database layer | Version: 1.9b1
(models, ORM) | Keywords: postgresql db
Severity: Normal | contenttypes
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Hi,
I'm the author of a small package, that allows you to filter
GenericForeignKey fields using custom query magic introduced in Django
1.7, https://github.com/mpasternak/djorm-ext-filtered-contenttypes/ . It
works on Django 1.7 and 1.8.
On 1.9 my package is impossible to implement. Reason:
https://github.com/django/django/commit/9ed82154bd0bd01c6195942db84302e791ad366f
which fixed https://code.djangoproject.com/ticket/23791 .
I realize, that the fix for #23791 is very important and I'm glad this bug
was solved. I have nothing against it and it's cool that it was
implemented; having OneToOne as a primary key seems an interesting use
case.
On the other hand, I'd love to be able to use my package on Django 1.9
without too much hackery (there's already some involved).
The reason for GenericForeignKey filtering and for that app of mine... in
PostgreSQL you can create a compound index of (content_type_id, object_id)
and use it for querying. If I can write Python code like:
{{{
StorageRecord.objects.filter(object__in=OtherModel.objects.filter(...))
}}}
... and my package can translate it to:
{{{
SELECT * FROM app_storage_record WHERE (content_type_id, object_id) IN
(SELECT content_type_id, object_id FROM app_other_model WHERE ... )
}}}
... then PostgreSQL will be able to use compound index on
(content_type_id, object_id) and the query will be insanely fast.
I use this to create a large cache table for my app, that holds records
from 5 other tables. It uses GenericForeignKey to hold references to those
tables. I use my FilteredGenericForeignKey field to filter stuff in that
big table. On PostgreSQL with reasonable indexes it is very fast.
If you happen to download my project, just please run tox and see the
problem. 1.7 and 1.8 work fine. On 1.9 I get bugs like:
{{{
======================================================================
ERROR: test_single_object
(filtered_contenttypes.tests.test_fields.TestFilteredContentTypes)
----------------------------------------------------------------------
Traceback (most recent call last):
File "../filtered_contenttypes/tests/test_fields.py", line 32, in
test_single_object
qry = StorageRecord.objects.filter(item=self.l)
File "/Users/mpasternak/Programowanie/djorm-ext-filtered-
contenttypes/.tox/py35-django19/lib/python3.5/site-
packages/django/db/models/manager.py", line 122, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "/Users/mpasternak/Programowanie/djorm-ext-filtered-
contenttypes/.tox/py35-django19/lib/python3.5/site-
packages/django/db/models/query.py", line 790, in filter
return self._filter_or_exclude(False, *args, **kwargs)
File "/Users/mpasternak/Programowanie/djorm-ext-filtered-
contenttypes/.tox/py35-django19/lib/python3.5/site-
packages/django/db/models/query.py", line 808, in _filter_or_exclude
clone.query.add_q(Q(*args, **kwargs))
File "/Users/mpasternak/Programowanie/djorm-ext-filtered-
contenttypes/.tox/py35-django19/lib/python3.5/site-
packages/django/db/models/sql/query.py", line 1240, in add_q
clause, _ = self._add_q(q_object, self.used_aliases)
File "/Users/mpasternak/Programowanie/djorm-ext-filtered-
contenttypes/.tox/py35-django19/lib/python3.5/site-
packages/django/db/models/sql/query.py", line 1266, in _add_q
allow_joins=allow_joins, split_subq=split_subq,
File "/Users/mpasternak/Programowanie/djorm-ext-filtered-
contenttypes/.tox/py35-django19/lib/python3.5/site-
packages/django/db/models/sql/query.py", line 1174, in build_filter
self.check_related_objects(field, value, opts)
File "/Users/mpasternak/Programowanie/djorm-ext-filtered-
contenttypes/.tox/py35-django19/lib/python3.5/site-
packages/django/db/models/sql/query.py", line 1071, in
check_related_objects
self.check_query_object_type(value, opts, field)
File "/Users/mpasternak/Programowanie/djorm-ext-filtered-
contenttypes/.tox/py35-django19/lib/python3.5/site-
packages/django/db/models/sql/query.py", line 1055, in
check_query_object_type
(value, opts.object_name))
ValueError: Cannot query "Laptop object": Must be "StorageRecord"
instance.
----------------------------------------------------------------------
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/25747>
Django <https://code.djangoproject.com/>
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