Fixed #26226 -- Made related managers honor the queryset used for prefetching their results.

Thanks Loïc for the suggested improvements and Tim for the review.

3 files changed, 60 insertions, 22 deletions

diff --git a/django/contrib/contenttypes/fields.py b/django/contrib/contenttypes/fields.py
index a51ecdd48e..f9d5d7cfd2 100644
--- a/django/contrib/contenttypes/fields.py
+++ b/django/contrib/contenttypes/fields.py
@@ -521,12 +521,19 @@ def create_generic_related_manager(superclass, rel):
         def __str__(self):
             return repr(self)
 
+        def _apply_rel_filters(self, queryset):
+            """
+            Filter the queryset for the instance this manager is bound to.
+            """
+            db = self._db or router.db_for_read(self.model, instance=self.instance)
+            return queryset.using(db).filter(**self.core_filters)
+
         def get_queryset(self):
             try:
                 return self.instance._prefetched_objects_cache[self.prefetch_cache_name]
             except (AttributeError, KeyError):
-                db = self._db or router.db_for_read(self.model, instance=self.instance)
-                return super(GenericRelatedObjectManager, self).get_queryset().using(db).filter(**self.core_filters)
+                queryset = super(GenericRelatedObjectManager, self).get_queryset()
+                return self._apply_rel_filters(queryset)
 
         def get_prefetch_queryset(self, instances, queryset=None):
             if queryset is None:
diff --git a/django/db/models/fields/related_descriptors.py b/django/db/models/fields/related_descriptors.py
index eae3a9628d..b6349e5c49 100644
--- a/django/db/models/fields/related_descriptors.py
+++ b/django/db/models/fields/related_descriptors.py
@@ -502,23 +502,29 @@ def create_reverse_many_to_one_manager(superclass, rel):
             return manager_class(self.instance)
         do_not_call_in_templates = True
 
+        def _apply_rel_filters(self, queryset):
+            """
+            Filter the queryset for the instance this manager is bound to.
+            """
+            db = self._db or router.db_for_read(self.model, instance=self.instance)
+            empty_strings_as_null = connections[db].features.interprets_empty_strings_as_nulls
+            queryset._add_hints(instance=self.instance)
+            if self._db:
+                queryset = queryset.using(self._db)
+            queryset = queryset.filter(**self.core_filters)
+            for field in self.field.foreign_related_fields:
+                val = getattr(self.instance, field.attname)
+                if val is None or (val == '' and empty_strings_as_null):
+                    return queryset.none()
+            queryset._known_related_objects = {self.field: {self.instance.pk: self.instance}}
+            return queryset
+
         def get_queryset(self):
             try:
                 return self.instance._prefetched_objects_cache[self.field.related_query_name()]
             except (AttributeError, KeyError):
-                db = self._db or router.db_for_read(self.model, instance=self.instance)
-                empty_strings_as_null = connections[db].features.interprets_empty_strings_as_nulls
-                qs = super(RelatedManager, self).get_queryset()
-                qs._add_hints(instance=self.instance)
-                if self._db:
-                    qs = qs.using(self._db)
-                qs = qs.filter(**self.core_filters)
-                for field in self.field.foreign_related_fields:
-                    val = getattr(self.instance, field.attname)
-                    if val is None or (val == '' and empty_strings_as_null):
-                        return qs.none()
-                qs._known_related_objects = {self.field: {self.instance.pk: self.instance}}
-                return qs
+                queryset = super(RelatedManager, self).get_queryset()
+                return self._apply_rel_filters(queryset)
 
         def get_prefetch_queryset(self, instances, queryset=None):
             if queryset is None:
@@ -776,15 +782,21 @@ def create_forward_many_to_many_manager(superclass, rel, reverse):
                 filters |= symmetrical_filters
             return filters
 
+        def _apply_rel_filters(self, queryset):
+            """
+            Filter the queryset for the instance this manager is bound to.
+            """
+            queryset._add_hints(instance=self.instance)
+            if self._db:
+                queryset = queryset.using(self._db)
+            return queryset._next_is_sticky().filter(**self.core_filters)
+
         def get_queryset(self):
             try:
                 return self.instance._prefetched_objects_cache[self.prefetch_cache_name]
             except (AttributeError, KeyError):
-                qs = super(ManyRelatedManager, self).get_queryset()
-                qs._add_hints(instance=self.instance)
-                if self._db:
-                    qs = qs.using(self._db)
-                return qs._next_is_sticky().filter(**self.core_filters)
+                queryset = super(ManyRelatedManager, self).get_queryset()
+                return self._apply_rel_filters(queryset)
 
         def get_prefetch_queryset(self, instances, queryset=None):
             if queryset is None:
diff --git a/django/db/models/query.py b/django/db/models/query.py
index 71e9ba9bda..85567e88ac 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -23,6 +23,7 @@ from django.db.models.query_utils import (
 )
 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 partition
 from django.utils.version import get_version
 
@@ -1608,6 +1609,9 @@ def prefetch_one_level(instances, prefetcher, lookup, level):
             msg = 'to_attr={} conflicts with a field on the {} model.'
             raise ValueError(msg.format(to_attr, model.__name__))
 
+    # Whether or not we're prefetching the last part of the lookup.
+    leaf = len(lookup.prefetch_through.split(LOOKUP_SEP)) - 1 == level
+
     for obj in instances:
         instance_attr_val = instance_attr(obj)
         vals = rel_obj_cache.get(instance_attr_val, [])
@@ -1621,8 +1625,23 @@ def prefetch_one_level(instances, prefetcher, lookup, level):
                 setattr(obj, to_attr, vals)
                 obj._prefetched_objects_cache[cache_name] = vals
             else:
-                # Cache in the QuerySet.all().
-                qs = getattr(obj, to_attr).all()
+                manager = getattr(obj, to_attr)
+                if leaf and lookup.queryset is not None:
+                    try:
+                        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
                 # We don't want the individual qs doing prefetch_related now,
                 # since we have merged this into the current work.