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seros1521 90257e9dee Fixes #8715: eliminates duplicates when used in many-to-many field constraints
When using permissions that use tags, a user may receive multiple permissions
of the same type if multiple tags are assigned to the device. This causes the
RestrictedQuerySet class to generate a query similar to this:

>>> dcim.models.Device.objects.filter(Q(tags__name='tag1')|Q(tags__name='tag2'))
<ConfigContextModelQuerySet [<Device: device1>, <Device: device1>]>

This query returns the same object twice if both tags are assigned to it. This
is due to the use of the django-taggit library. The library's documentation
describes this behavior as expected and suggests using an explicit distinct()
call in queries to avoid duplicates.

However, the use of DISTINCT in queries has a global side effect -
deduplication of responses, which may or may not be acceptable behavior
(depending on further use). Since it is not known how RestrictedQuerySet will
be used in the rest of the code, it was decided to dedupe using a subquery.
2022-03-04 14:37:05 +07:00

51 lines
2.0 KiB
Python

from django.db.models import Q, QuerySet
from utilities.permissions import permission_is_exempt
class RestrictedQuerySet(QuerySet):
def restrict(self, user, action='view'):
"""
Filter the QuerySet to return only objects on which the specified user has been granted the specified
permission.
:param user: User instance
:param action: The action which must be permitted (e.g. "view" for "dcim.view_site"); default is 'view'
"""
# Resolve the full name of the required permission
app_label = self.model._meta.app_label
model_name = self.model._meta.model_name
permission_required = f'{app_label}.{action}_{model_name}'
# Bypass restriction for superusers and exempt views
if user.is_superuser or permission_is_exempt(permission_required):
qs = self
# User is anonymous or has not been granted the requisite permission
elif not user.is_authenticated or permission_required not in user.get_all_permissions():
qs = self.none()
# Filter the queryset to include only objects with allowed attributes
else:
attrs = Q()
for perm_attrs in user._object_perm_cache[permission_required]:
if type(perm_attrs) is list:
for p in perm_attrs:
attrs |= Q(**p)
elif perm_attrs:
attrs |= Q(**perm_attrs)
else:
# Any permission with null constraints grants access to _all_ instances
attrs = Q()
break
else:
# for else, when no break
# avoid duplicates when JOIN on many-to-many fields without using DISTINCT.
# DISTINCT acts globally on the entire request, which may not be desirable.
allowed_objects = self.model.objects.filter(attrs)
attrs = Q(pk__in=allowed_objects)
qs = self.filter(attrs)
return qs