Refs #26226 -- Removed support for related manager classes without a _apply_rel_filters() method.

Per deprecation timeline.

django/db/models/query.py

@@ -22,7 +22,6 @@ from django.db.models.functions import Trunc
 from django.db.models.query_utils import InvalidQuery, Q
 from django.db.models.sql.constants import CURSOR
 from django.utils import six, timezone
-from django.utils.deprecation import RemovedInDjango20Warning
 from django.utils.functional import cached_property, partition
 from django.utils.version import get_version
 
@@ -1613,19 +1612,7 @@ def prefetch_one_level(instances, prefetcher, lookup, level):
             else:
                 manager = getattr(obj, to_attr)
                 if leaf and lookup.queryset is not None:
-                    try:
+                    qs = manager._apply_rel_filters(lookup.queryset)
-                        apply_rel_filter = manager._apply_rel_filters
-                    except AttributeError:
-                        warnings.warn(
-                            "The `%s.%s` class must implement a `_apply_rel_filters()` "
-                            "method that accepts a `QuerySet` as its single "
-                            "argument and returns an appropriately filtered version "
-                            "of it." % (manager.__class__.__module__, manager.__class__.__name__),
-                            RemovedInDjango20Warning,
-                        )
-                        qs = manager.get_queryset()
-                    else:
-                        qs = apply_rel_filter(lookup.queryset)
                 else:
                     qs = manager.get_queryset()
                 qs._result_cache = vals

docs/releases/2.0.txt

@@ -355,3 +355,6 @@ these features.
   ``Meta.default_related_name`` is set is removed.
 
 * The MySQL ``__search`` lookup is removed.
+
+* The shim for supporting custom related manager classes without a
+  ``_apply_rel_filters()`` method is removed.

tests/prefetch_related/tests.py

@@ -1,7 +1,5 @@
 from __future__ import unicode_literals
 
-import warnings
-
 from django.contrib.contenttypes.models import ContentType
 from django.core.exceptions import ObjectDoesNotExist
 from django.db import connection
@@ -711,30 +709,6 @@ class CustomPrefetchTests(TestCase):
             self.room2_1
         )
 
-    def test_apply_rel_filters_deprecation_shim(self):
-        # Simulate a missing `_apply_rel_filters` method.
-        del Person.houses.related_manager_cls._apply_rel_filters
-        # Also remove `get_queryset` as it rely on `_apply_rel_filters`.
-        del Person.houses.related_manager_cls.get_queryset
-        try:
-            with warnings.catch_warnings(record=True) as warns:
-                warnings.simplefilter('always')
-                list(Person.objects.prefetch_related(
-                    Prefetch('houses', queryset=House.objects.filter(name='House 1'))
-                ))
-        finally:
-            # Deleting `related_manager_cls` will force the creation of a new
-            # class since it's a `cached_property`.
-            del Person.houses.related_manager_cls
-        msg = (
-            'The `django.db.models.fields.related_descriptors.ManyRelatedManager` class '
-            'must implement a `_apply_rel_filters()` method that accepts a `QuerySet` as '
-            'its single argument and returns an appropriately filtered version of it.'
-        )
-        self.assertEqual(len(warns), 2)  # Once person.
-        self.assertEqual(str(warns[0].message), msg)
-        self.assertEqual(str(warns[0].message), msg)
-
     def test_values_queryset(self):
         with self.assertRaisesMessage(ValueError, 'Prefetch querysets cannot use values().'):
             Prefetch('houses', House.objects.values('pk'))