Fixed #23550 -- Normalized get_queryset() of RelatedObjectDescriptor

and ReverseSingleRelatedObjectDescriptor so they actually return QuerySet
instances.

Also ensured that SingleRelatedObjectDescriptor.get_queryset() accounts
for use_for_related_fields=True.

This cleanup lays the groundwork for #23533.

Thanks Anssi Kääriäinen for the review.

django/db/models/fields/related.py

@@ -370,14 +370,16 @@ class SingleRelatedObjectDescriptor(object):
         return hasattr(instance, self.cache_name)
 
     def get_queryset(self, **hints):
-        # Gotcha: we return a `Manager` instance (i.e. not a `QuerySet`)!
-        return self.related.model._base_manager.db_manager(hints=hints)
+        manager = self.related.model._default_manager
+        # If the related manager indicates that it should be used for
+        # related fields, respect that.
+        if not getattr(manager, 'use_for_related_fields', False):
+            manager = self.related.model._base_manager
+        return manager.db_manager(hints=hints).all()
 
     def get_prefetch_queryset(self, instances, queryset=None):
         if queryset is None:
-            # Despite its name `get_queryset()` returns an instance of
-            # `Manager`, therefore we call `all()` to normalize to `QuerySet`.
-            queryset = self.get_queryset().all()
+            queryset = self.get_queryset()
         queryset._add_hints(instance=instances[0])
 
         rel_obj_attr = attrgetter(self.related.field.attname)
@@ -499,20 +501,16 @@ class ReverseSingleRelatedObjectDescriptor(object):
         return hasattr(instance, self.cache_name)
 
     def get_queryset(self, **hints):
-        rel_mgr = self.field.rel.to._default_manager.db_manager(hints=hints)
+        manager = self.field.rel.to._default_manager
         # If the related manager indicates that it should be used for
         # related fields, respect that.
-        if getattr(rel_mgr, 'use_for_related_fields', False):
-            # Gotcha: we return a `Manager` instance (i.e. not a `QuerySet`)!
-            return rel_mgr
-        else:
-            return QuerySet(self.field.rel.to, hints=hints)
+        if not getattr(manager, 'use_for_related_fields', False):
+            manager = self.field.rel.to._base_manager
+        return manager.db_manager(hints=hints).all()
 
     def get_prefetch_queryset(self, instances, queryset=None):
         if queryset is None:
-            # Despite its name `get_queryset()` may return an instance of
-            # `Manager`, therefore we call `all()` to normalize to `QuerySet`.
-            queryset = self.get_queryset().all()
+            queryset = self.get_queryset()
         queryset._add_hints(instance=instances[0])
 
         rel_obj_attr = self.field.get_foreign_related_value

tests/one_to_one/models.py

@@ -96,3 +96,24 @@ class Pointer2(models.Model):
 
 class HiddenPointer(models.Model):
     target = models.OneToOneField(Target, related_name='hidden+')
+
+
+# Test related objects visibility.
+class SchoolManager(models.Manager):
+    def get_queryset(self):
+        return super(SchoolManager, self).get_queryset().filter(is_public=True)
+
+
+class School(models.Model):
+    is_public = models.BooleanField(default=False)
+    objects = SchoolManager()
+
+
+class DirectorManager(models.Manager):
+    def get_queryset(self):
+        return super(DirectorManager, self).get_queryset().filter(is_temp=False)
+
+class Director(models.Model):
+    is_temp = models.BooleanField(default=False)
+    school = models.OneToOneField(School)
+    objects = DirectorManager()

tests/one_to_one/tests.py

@@ -4,7 +4,7 @@ from django.db import transaction, IntegrityError, connection
 from django.test import TestCase
 
 from .models import (Bar, Favorites, HiddenPointer, ManualPrimaryKey, MultiModel,
-    Place, RelatedModel, Restaurant, Target, UndergroundBar, Waiter)
+    Place, RelatedModel, Restaurant, School, Director, Target, UndergroundBar, Waiter)
 
 
 class OneToOneTests(TestCase):
@@ -382,3 +382,59 @@ class OneToOneTests(TestCase):
         self.assertFalse(
             hasattr(Target, HiddenPointer._meta.get_field('target').related.get_accessor_name())
         )
+
+    def test_related_object(self):
+        public_school = School.objects.create(is_public=True)
+        public_director = Director.objects.create(school=public_school, is_temp=False)
+
+        private_school = School.objects.create(is_public=False)
+        private_director = Director.objects.create(school=private_school, is_temp=True)
+
+        # Only one school is available via all() due to the custom default manager.
+        self.assertQuerysetEqual(
+            School.objects.all(),
+            ["<School: School object>"]
+        )
+
+        # Only one director is available via all() due to the custom default manager.
+        self.assertQuerysetEqual(
+            Director.objects.all(),
+            ["<Director: Director object>"]
+        )
+
+        self.assertEqual(public_director.school, public_school)
+        self.assertEqual(public_school.director, public_director)
+
+        # Make sure the base manager is used so that the related objects
+        # is still accessible even if the default manager doesn't normally
+        # allow it.
+        self.assertEqual(private_director.school, private_school)
+
+        # Make sure the base manager is used so that an student can still access
+        # its related school even if the default manager doesn't normally
+        # allow it.
+        self.assertEqual(private_school.director, private_director)
+
+        # If the manager is marked "use_for_related_fields", it'll get used instead
+        # of the "bare" queryset. Usually you'd define this as a property on the class,
+        # but this approximates that in a way that's easier in tests.
+        School.objects.use_for_related_fields = True
+        try:
+            private_director = Director._base_manager.get(pk=private_director.pk)
+            self.assertRaises(School.DoesNotExist, lambda: private_director.school)
+        finally:
+            School.objects.use_for_related_fields = False
+
+        Director.objects.use_for_related_fields = True
+        try:
+            private_school = School._base_manager.get(pk=private_school.pk)
+            self.assertRaises(Director.DoesNotExist, lambda: private_school.director)
+        finally:
+            Director.objects.use_for_related_fields = False
+
+    def test_hasattr_related_object(self):
+        # The exception raised on attribute access when a related object
+        # doesn't exist should be an instance of a subclass of `AttributeError`
+        # refs #21563
+        self.assertFalse(hasattr(Director(), 'director'))
+        self.assertFalse(hasattr(School(), 'school'))