Refs #28586 -- Copied fetch modes to related objects.

This change ensures that behavior and performance remain consistent when
traversing relationships.

django/contrib/contenttypes/fields.py

@@ -201,11 +201,13 @@ class GenericForeignKeyDescriptor:
         for ct_id, fkeys in fk_dict.items():
             if ct_id in custom_queryset_dict:
                 # Return values from the custom queryset, if provided.
-                ret_val.extend(custom_queryset_dict[ct_id].filter(pk__in=fkeys))
+                queryset = custom_queryset_dict[ct_id].filter(pk__in=fkeys)
             else:
                 instance = instance_dict[ct_id]
                 ct = self.field.get_content_type(id=ct_id, using=instance._state.db)
-                ret_val.extend(ct.get_all_objects_for_this_type(pk__in=fkeys))
+                queryset = ct.get_all_objects_for_this_type(pk__in=fkeys)
+
+            ret_val.extend(queryset.fetch_mode(instances[0]._state.fetch_mode))
 
         # For doing the join in Python, we have to match both the FK val and
         # the content type, so we use a callable that returns a (fk, class)
@@ -271,6 +273,8 @@ class GenericForeignKeyDescriptor:
                 )
             except ObjectDoesNotExist:
                 pass
+            else:
+                rel_obj._state.fetch_mode = instance._state.fetch_mode
         self.field.set_cached_value(instance, rel_obj)
 
     def fetch_many(self, instances):
@@ -636,7 +640,11 @@ def create_generic_related_manager(superclass, rel):
             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)
+            return (
+                queryset.using(db)
+                .fetch_mode(self.instance._state.fetch_mode)
+                .filter(**self.core_filters)
+            )
 
         def _remove_prefetched_objects(self):
             try:

django/db/models/fields/related_descriptors.py

@@ -169,7 +169,7 @@ class ForwardManyToOneDescriptor:
     def get_queryset(self, *, instance):
         return self.field.remote_field.model._base_manager.db_manager(
             hints={"instance": instance}
-        ).all()
+        ).fetch_mode(instance._state.fetch_mode)
 
     def get_prefetch_querysets(self, instances, querysets=None):
         if querysets and len(querysets) != 1:
@@ -398,6 +398,7 @@ class ForwardOneToOneDescriptor(ForwardManyToOneDescriptor):
                 obj = rel_model(**kwargs)
                 obj._state.adding = instance._state.adding
                 obj._state.db = instance._state.db
+                obj._state.fetch_mode = instance._state.fetch_mode
                 return obj
         return super().get_object(instance)
 
@@ -462,7 +463,7 @@ class ReverseOneToOneDescriptor:
     def get_queryset(self, *, instance):
         return self.related.related_model._base_manager.db_manager(
             hints={"instance": instance}
-        ).all()
+        ).fetch_mode(instance._state.fetch_mode)
 
     def get_prefetch_querysets(self, instances, querysets=None):
         if querysets and len(querysets) != 1:
@@ -740,6 +741,7 @@ def create_reverse_many_to_one_manager(superclass, rel):
             queryset._add_hints(instance=self.instance)
             if self._db:
                 queryset = queryset.using(self._db)
+            queryset._fetch_mode = self.instance._state.fetch_mode
             queryset._defer_next_filter = True
             queryset = queryset.filter(**self.core_filters)
             for field in self.field.foreign_related_fields:
@@ -1141,6 +1143,7 @@ def create_forward_many_to_many_manager(superclass, rel, reverse):
             queryset._add_hints(instance=self.instance)
             if self._db:
                 queryset = queryset.using(self._db)
+            queryset._fetch_mode = self.instance._state.fetch_mode
             queryset._defer_next_filter = True
             return queryset._next_is_sticky().filter(**self.core_filters)
 

django/db/models/query.py

@@ -90,6 +90,7 @@ class ModelIterable(BaseIterable):
         queryset = self.queryset
         db = queryset.db
         compiler = queryset.query.get_compiler(using=db)
+        fetch_mode = queryset._fetch_mode
         # Execute the query. This will also fill compiler.select, klass_info,
         # and annotations.
         results = compiler.execute_sql(
@@ -106,7 +107,7 @@ class ModelIterable(BaseIterable):
         init_list = [
             f[0].target.attname for f in select[model_fields_start:model_fields_end]
         ]
-        related_populators = get_related_populators(klass_info, select, db)
+        related_populators = get_related_populators(klass_info, select, db, fetch_mode)
         known_related_objects = [
             (
                 field,
@@ -124,7 +125,6 @@ class ModelIterable(BaseIterable):
             )
             for field, related_objs in queryset._known_related_objects.items()
         ]
-        fetch_mode = queryset._fetch_mode
         peers = []
         for row in compiler.results_iter(results):
             obj = model_cls.from_db(
@@ -2787,8 +2787,9 @@ class RelatedPopulator:
     model instance.
     """
 
-    def __init__(self, klass_info, select, db):
+    def __init__(self, klass_info, select, db, fetch_mode):
         self.db = db
+        self.fetch_mode = fetch_mode
         # Pre-compute needed attributes. The attributes are:
         #  - model_cls: the possibly deferred model class to instantiate
         #  - either:
@@ -2841,7 +2842,9 @@ class RelatedPopulator:
         # relationship. Therefore checking for a single member of the primary
         # key is enough to determine if the referenced object exists or not.
         self.pk_idx = self.init_list.index(self.model_cls._meta.pk_fields[0].attname)
-        self.related_populators = get_related_populators(klass_info, select, self.db)
+        self.related_populators = get_related_populators(
+            klass_info, select, self.db, fetch_mode
+        )
         self.local_setter = klass_info["local_setter"]
         self.remote_setter = klass_info["remote_setter"]
 
@@ -2853,7 +2856,12 @@ class RelatedPopulator:
         if obj_data[self.pk_idx] is None:
             obj = None
         else:
-            obj = self.model_cls.from_db(self.db, self.init_list, obj_data)
+            obj = self.model_cls.from_db(
+                self.db,
+                self.init_list,
+                obj_data,
+                fetch_mode=self.fetch_mode,
+            )
             for rel_iter in self.related_populators:
                 rel_iter.populate(row, obj)
         self.local_setter(from_obj, obj)
@@ -2861,10 +2869,10 @@ class RelatedPopulator:
             self.remote_setter(obj, from_obj)
 
 
-def get_related_populators(klass_info, select, db):
+def get_related_populators(klass_info, select, db, fetch_mode):
     iterators = []
     related_klass_infos = klass_info.get("related_klass_infos", [])
     for rel_klass_info in related_klass_infos:
-        rel_cls = RelatedPopulator(rel_klass_info, select, db)
+        rel_cls = RelatedPopulator(rel_klass_info, select, db, fetch_mode)
         iterators.append(rel_cls)
     return iterators

docs/topics/db/fetch-modes.txt

@@ -29,6 +29,11 @@ Fetch modes apply to:
 * Fields deferred with :meth:`.QuerySet.defer` or :meth:`.QuerySet.only`
 * :ref:`generic-relations`
 
+Django copies the fetch mode of an instance to any related objects it fetches,
+so the mode applies to a whole tree of relationships, not just the top-level
+model in the initial ``QuerySet``. This copying is also done in related
+managers, even though fetch modes don't affect such managers' queries.
+
 Available modes
 ===============
 

tests/foreign_object/tests.py

@@ -5,6 +5,7 @@ from operator import attrgetter
 
 from django.core.exceptions import FieldError, ValidationError
 from django.db import connection, models
+from django.db.models import FETCH_PEERS
 from django.test import SimpleTestCase, TestCase, skipUnlessDBFeature
 from django.test.utils import CaptureQueriesContext, isolate_apps
 from django.utils import translation
@@ -603,6 +604,42 @@ class MultiColumnFKTests(TestCase):
             [m4],
         )
 
+    def test_fetch_mode_copied_forward_fetching_one(self):
+        person = Person.objects.fetch_mode(FETCH_PEERS).get(pk=self.bob.pk)
+        self.assertEqual(person._state.fetch_mode, FETCH_PEERS)
+        self.assertEqual(
+            person.person_country._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
+    def test_fetch_mode_copied_forward_fetching_many(self):
+        people = list(Person.objects.fetch_mode(FETCH_PEERS))
+        person = people[0]
+        self.assertEqual(person._state.fetch_mode, FETCH_PEERS)
+        self.assertEqual(
+            person.person_country._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
+    def test_fetch_mode_copied_reverse_fetching_one(self):
+        country = Country.objects.fetch_mode(FETCH_PEERS).get(pk=self.usa.pk)
+        self.assertEqual(country._state.fetch_mode, FETCH_PEERS)
+        person = country.person_set.get(pk=self.bob.pk)
+        self.assertEqual(
+            person._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
+    def test_fetch_mode_copied_reverse_fetching_many(self):
+        countries = list(Country.objects.fetch_mode(FETCH_PEERS))
+        country = countries[0]
+        self.assertEqual(country._state.fetch_mode, FETCH_PEERS)
+        person = country.person_set.earliest("pk")
+        self.assertEqual(
+            person._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
 
 class TestModelCheckTests(SimpleTestCase):
     @isolate_apps("foreign_object")

tests/generic_relations/tests.py

@@ -813,7 +813,6 @@ class GenericRelationsTests(TestCase):
             self.assertEqual(quartz_tag.content_object, self.quartz)
 
     def test_fetch_mode_raise(self):
-        TaggedItem.objects.create(tag="lion", content_object=self.lion)
         tag = TaggedItem.objects.fetch_mode(RAISE).get(tag="yellow")
         msg = "Fetching of TaggedItem.content_object blocked."
         with self.assertRaisesMessage(FieldFetchBlocked, msg) as cm:
@@ -821,6 +820,37 @@ class GenericRelationsTests(TestCase):
         self.assertIsNone(cm.exception.__cause__)
         self.assertTrue(cm.exception.__suppress_context__)
 
+    def test_fetch_mode_copied_forward_fetching_one(self):
+        tag = TaggedItem.objects.fetch_mode(FETCH_PEERS).get(tag="yellow")
+        self.assertEqual(tag.content_object, self.lion)
+        self.assertEqual(
+            tag.content_object._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
+    def test_fetch_mode_copied_forward_fetching_many(self):
+        tags = list(TaggedItem.objects.fetch_mode(FETCH_PEERS).order_by("tag"))
+        tag = [t for t in tags if t.tag == "yellow"][0]
+        self.assertEqual(tag.content_object, self.lion)
+        self.assertEqual(
+            tag.content_object._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
+    def test_fetch_mode_copied_reverse_fetching_one(self):
+        animal = Animal.objects.fetch_mode(FETCH_PEERS).get(pk=self.lion.pk)
+        self.assertEqual(animal._state.fetch_mode, FETCH_PEERS)
+        tag = animal.tags.get(tag="yellow")
+        self.assertEqual(tag._state.fetch_mode, FETCH_PEERS)
+
+    def test_fetch_mode_copied_reverse_fetching_many(self):
+        animals = list(Animal.objects.fetch_mode(FETCH_PEERS))
+        animal = animals[0]
+        self.assertEqual(animal._state.fetch_mode, FETCH_PEERS)
+        tags = list(animal.tags.all())
+        tag = tags[0]
+        self.assertEqual(tag._state.fetch_mode, FETCH_PEERS)
+
 
 class ProxyRelatedModelTest(TestCase):
     def test_default_behavior(self):

tests/many_to_many/tests.py

@@ -1,6 +1,7 @@
 from unittest import mock
 
 from django.db import connection, transaction
+from django.db.models import FETCH_PEERS
 from django.test import TestCase, skipIfDBFeature, skipUnlessDBFeature
 
 from .models import (
@@ -589,6 +590,46 @@ class ManyToManyTests(TestCase):
                 querysets=[Publication.objects.all(), Publication.objects.all()],
             )
 
+    def test_fetch_mode_copied_forward_fetching_one(self):
+        a = Article.objects.fetch_mode(FETCH_PEERS).get(pk=self.a1.pk)
+        self.assertEqual(a._state.fetch_mode, FETCH_PEERS)
+        p = a.publications.earliest("pk")
+        self.assertEqual(
+            p._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
+    def test_fetch_mode_copied_forward_fetching_many(self):
+        articles = list(Article.objects.fetch_mode(FETCH_PEERS))
+        a = articles[0]
+        self.assertEqual(a._state.fetch_mode, FETCH_PEERS)
+        publications = list(a.publications.all())
+        p = publications[0]
+        self.assertEqual(
+            p._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
+    def test_fetch_mode_copied_reverse_fetching_one(self):
+        p1 = Publication.objects.fetch_mode(FETCH_PEERS).get(pk=self.p1.pk)
+        self.assertEqual(p1._state.fetch_mode, FETCH_PEERS)
+        a = p1.article_set.earliest("pk")
+        self.assertEqual(
+            a._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
+    def test_fetch_mode_copied_reverse_fetching_many(self):
+        publications = list(Publication.objects.fetch_mode(FETCH_PEERS))
+        p = publications[0]
+        self.assertEqual(p._state.fetch_mode, FETCH_PEERS)
+        articles = list(p.article_set.all())
+        a = articles[0]
+        self.assertEqual(
+            a._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
 
 class ManyToManyQueryTests(TestCase):
     """

tests/many_to_one/tests.py

@@ -941,3 +941,52 @@ class ManyToOneTests(TestCase):
             a.reporter
         self.assertIsNone(cm.exception.__cause__)
         self.assertTrue(cm.exception.__suppress_context__)
+
+    def test_fetch_mode_copied_forward_fetching_one(self):
+        a1 = Article.objects.fetch_mode(FETCH_PEERS).get()
+        self.assertEqual(a1._state.fetch_mode, FETCH_PEERS)
+        self.assertEqual(
+            a1.reporter._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
+    def test_fetch_mode_copied_forward_fetching_many(self):
+        Article.objects.create(
+            headline="This is another test",
+            pub_date=datetime.date(2005, 7, 27),
+            reporter=self.r2,
+        )
+        a1, a2 = Article.objects.fetch_mode(FETCH_PEERS)
+        self.assertEqual(a1._state.fetch_mode, FETCH_PEERS)
+        self.assertEqual(
+            a1.reporter._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
+    def test_fetch_mode_copied_reverse_fetching_one(self):
+        r1 = Reporter.objects.fetch_mode(FETCH_PEERS).get(pk=self.r.pk)
+        self.assertEqual(r1._state.fetch_mode, FETCH_PEERS)
+        article = r1.article_set.get()
+        self.assertEqual(
+            article._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
+    def test_fetch_mode_copied_reverse_fetching_many(self):
+        Article.objects.create(
+            headline="This is another test",
+            pub_date=datetime.date(2005, 7, 27),
+            reporter=self.r2,
+        )
+        r1, r2 = Reporter.objects.fetch_mode(FETCH_PEERS)
+        self.assertEqual(r1._state.fetch_mode, FETCH_PEERS)
+        a1 = r1.article_set.get()
+        self.assertEqual(
+            a1._state.fetch_mode,
+            FETCH_PEERS,
+        )
+        a2 = r2.article_set.get()
+        self.assertEqual(
+            a2._state.fetch_mode,
+            FETCH_PEERS,
+        )

tests/model_inheritance_regress/tests.py

@@ -7,6 +7,7 @@ from operator import attrgetter
 from unittest import expectedFailure
 
 from django import forms
+from django.db.models import FETCH_PEERS
 from django.test import TestCase
 
 from .models import (
@@ -600,6 +601,22 @@ class ModelInheritanceTest(TestCase):
             self.assertEqual(restaurant.place_ptr.restaurant, restaurant)
             self.assertEqual(restaurant.italianrestaurant, italian_restaurant)
 
+    def test_parent_access_copies_fetch_mode(self):
+        italian_restaurant = ItalianRestaurant.objects.create(
+            name="Mom's Spaghetti",
+            address="2131 Woodward Ave",
+            serves_hot_dogs=False,
+            serves_pizza=False,
+            serves_gnocchi=True,
+        )
+
+        # No queries are made when accessing the parent objects.
+        italian_restaurant = ItalianRestaurant.objects.fetch_mode(FETCH_PEERS).get(
+            pk=italian_restaurant.pk
+        )
+        restaurant = italian_restaurant.restaurant_ptr
+        self.assertEqual(restaurant._state.fetch_mode, FETCH_PEERS)
+
     def test_id_field_update_on_ancestor_change(self):
         place1 = Place.objects.create(name="House of Pasta", address="944 Fullerton")
         place2 = Place.objects.create(name="House of Pizza", address="954 Fullerton")

tests/one_to_one/tests.py

@@ -657,3 +657,41 @@ class OneToOneTests(TestCase):
             p.restaurant
         self.assertIsNone(cm.exception.__cause__)
         self.assertTrue(cm.exception.__suppress_context__)
+
+    def test_fetch_mode_copied_forward_fetching_one(self):
+        r1 = Restaurant.objects.fetch_mode(FETCH_PEERS).get(pk=self.r1.pk)
+        self.assertEqual(r1._state.fetch_mode, FETCH_PEERS)
+        self.assertEqual(
+            r1.place._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
+    def test_fetch_mode_copied_forward_fetching_many(self):
+        Restaurant.objects.create(
+            place=self.p2, serves_hot_dogs=True, serves_pizza=False
+        )
+        r1, r2 = Restaurant.objects.fetch_mode(FETCH_PEERS)
+        self.assertEqual(r1._state.fetch_mode, FETCH_PEERS)
+        self.assertEqual(
+            r1.place._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
+    def test_fetch_mode_copied_reverse_fetching_one(self):
+        p1 = Place.objects.fetch_mode(FETCH_PEERS).get(pk=self.p1.pk)
+        self.assertEqual(p1._state.fetch_mode, FETCH_PEERS)
+        self.assertEqual(
+            p1.restaurant._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
+    def test_fetch_mode_copied_reverse_fetching_many(self):
+        Restaurant.objects.create(
+            place=self.p2, serves_hot_dogs=True, serves_pizza=False
+        )
+        p1, p2 = Place.objects.fetch_mode(FETCH_PEERS)
+        self.assertEqual(p1._state.fetch_mode, FETCH_PEERS)
+        self.assertEqual(
+            p1.restaurant._state.fetch_mode,
+            FETCH_PEERS,
+        )

tests/prefetch_related/tests.py

@@ -3,7 +3,13 @@ from unittest import mock
 from django.contrib.contenttypes.models import ContentType
 from django.core.exceptions import ObjectDoesNotExist
 from django.db import NotSupportedError, connection
-from django.db.models import F, Prefetch, QuerySet, prefetch_related_objects
+from django.db.models import (
+    FETCH_PEERS,
+    F,
+    Prefetch,
+    QuerySet,
+    prefetch_related_objects,
+)
 from django.db.models.fetch_modes import RAISE
 from django.db.models.query import get_prefetcher
 from django.db.models.sql import Query
@@ -108,6 +114,28 @@ class PrefetchRelatedTests(TestDataMixin, TestCase):
         normal_books = [a.first_book for a in Author.objects.all()]
         self.assertEqual(books, normal_books)
 
+    def test_fetch_mode_copied_fetching_one(self):
+        author = (
+            Author.objects.fetch_mode(FETCH_PEERS)
+            .prefetch_related("first_book")
+            .get(pk=self.author1.pk)
+        )
+        self.assertEqual(author._state.fetch_mode, FETCH_PEERS)
+        self.assertEqual(
+            author.first_book._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
+    def test_fetch_mode_copied_fetching_many(self):
+        authors = list(
+            Author.objects.fetch_mode(FETCH_PEERS).prefetch_related("first_book")
+        )
+        self.assertEqual(authors[0]._state.fetch_mode, FETCH_PEERS)
+        self.assertEqual(
+            authors[0].first_book._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
     def test_fetch_mode_raise(self):
         authors = list(Author.objects.fetch_mode(RAISE).prefetch_related("first_book"))
         authors[0].first_book  # No exception, already loaded

tests/select_related/tests.py

@@ -1,4 +1,5 @@
 from django.core.exceptions import FieldError
+from django.db.models import FETCH_PEERS
 from django.test import SimpleTestCase, TestCase
 
 from .models import (
@@ -210,6 +211,37 @@ class SelectRelatedTests(TestCase):
         with self.assertRaisesMessage(TypeError, message):
             list(Species.objects.values_list("name").select_related("genus"))
 
+    def test_fetch_mode_copied_fetching_one(self):
+        fly = (
+            Species.objects.fetch_mode(FETCH_PEERS)
+            .select_related("genus__family")
+            .get(name="melanogaster")
+        )
+        self.assertEqual(fly._state.fetch_mode, FETCH_PEERS)
+        self.assertEqual(
+            fly.genus._state.fetch_mode,
+            FETCH_PEERS,
+        )
+        self.assertEqual(
+            fly.genus.family._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
+    def test_fetch_mode_copied_fetching_many(self):
+        specieses = list(
+            Species.objects.fetch_mode(FETCH_PEERS).select_related("genus__family")
+        )
+        species = specieses[0]
+        self.assertEqual(species._state.fetch_mode, FETCH_PEERS)
+        self.assertEqual(
+            species.genus._state.fetch_mode,
+            FETCH_PEERS,
+        )
+        self.assertEqual(
+            species.genus.family._state.fetch_mode,
+            FETCH_PEERS,
+        )
+
 
 class SelectRelatedValidationTests(SimpleTestCase):
     """