#18005: Add support for ManyToManyFields on proxy models
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Reporter: Bradley Ayers <bradley.ayers@…> | Owner: nobody
Type: New feature | Status: new
Component: Database layer (models, ORM) | Version: 1.4
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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It appears Django already supports this, but explicitly checks for and
prevents it from working:
https://code.djangoproject.com/browser/django/trunk/django/db/models/base.py#L123
{{{
if (new_class._meta.local_fields:
or new_class._meta.local_many_to_many):
raise FieldError("Proxy model '%s' contains model fields." % name)
}}}
By simply removing the second half of the condition, ``ManyToManyField``s
work on
proxy models.
In my current project I'm proxying the ``auth.User`` as ``users.User``,
and I want to add a M2M
relationship to ``core.District``. I don't want to modify core, so I'd
like to
add the relationship to the ``users.User`` proxy model:
{{{
from django.contrib.auth.models import User as AuthUser
class User(AuthUser):
districts = models.ManyToManyField("core.District")
class Meta:
proxy = True
}}}
Running ``./manage.py sql users`` shows that the correct SQL is generated:
{{{
BEGIN;
CREATE TABLE "users_user_districts" (
"id" integer NOT NULL PRIMARY KEY,
"user_id" integer NOT NULL,
"district_id" integer NOT NULL REFERENCES "core_district" ("id"),
UNIQUE ("user_id", "district_id")
)
;
COMMIT;
}}}
I wrote a crude test case, and it all seems to work:
{{{
user = User.objects.create_user("username", "f...@example.com",
"password")
district = District.objects.create(name="Foo")
user.districts.add(district)
user = User.objects.get(pk=user.pk) # use fresh version
assert district.users.count() == 1
assert district.users.all()[0].pk == user.pk
user.districts.clear()
user = User.objects.get(pk=user.pk) # use fresh version
assert user.districts.count() == 0
assert list(user.districts.all()) == []
}}}
The Django test suite passes using SQLite:
{{{
$ ./runtests.py --settings=test_sqlite
Creating test database for alias 'default'...
Creating test database for alias 'other'...
...<snip>....
----------------------------------------------------------------------
Ran 4657 tests in 1007.250s
OK (skipped=115, expected failures=2)
Destroying test database for alias 'default'...
Destroying test database for alias 'other'...
}}}
Are there any arguments against this?
--
Ticket URL: <https://code.djangoproject.com/ticket/18005>
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