#35792: Enhance _get_group_permissions method of ModelBackend
-------------------------------------+-------------------------------------
Reporter: Bona Fide IT GmbH | Type:
| Cleanup/optimization
Status: new | Component:
| contrib.auth
Version: 4.2 | Severity: Normal
Keywords: Backend | Triage Stage:
| Unreviewed
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
We would like to suggest a change to the `_get_group_permissions` method
in the django `ModelBackend`.
The current code gets the registered `User` model and from it the `groups`
field to get the related query name to compose a filter query for the
`Permission` model at the end.
{{{#!div style="font-size: 80%"
Current version of `django/contrib/auth/backends.py`
(https://github.com/django/django/blob/main/django/contrib/auth/backends.py#L61-L64)
:
{{{#!python
from django.contrib.auth import get_user_model
from django.contrib.auth.models import Permission
from django.db.models import Exists, OuterRef, Q
UserModel = get_user_model()
...
class ModelBackend(BaseBackend):
...
def _get_group_permissions(self, user_obj):
user_groups_field = get_user_model()._meta.get_field("groups")
user_groups_query = "group__%s" %
user_groups_field.related_query_name()
return Permission.objects.filter(**{user_groups_query: user_obj})
...
}}}
}}}
Since in this method both the `group` field of the `Permission` model and
the reverse relation field `groups` of the [custom] `User` model are fixed
anyway, we suggest the following change.
{{{#!div style="font-size: 80%"
{{{#!python
class ModelBackend(BaseBackend):
...
def _get_group_permissions(self, user_obj):
return Permission.objects.filter(group__in=user_obj.groups.all())
...
}}}
}}}
We are not sure if this will fundamentally change the performance of the
query, but it seems to us to be a simpler variant than going via `_meta`
and then constructing a query string that is fixed anyway.
A further argument from our side is that this would probably also make it
possible to use a custom `Group` model and to solve problems such as those
mentioned here: https://github.com/django-guardian/django-
guardian/pull/504#issuecomment-429810401 without introducing something
like an `AUTH_GROUP_MODEL` setting.
--
Ticket URL: <https://code.djangoproject.com/ticket/35792>
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