Fixed #28586 -- Added model field fetch modes.

May your database queries be much reduced with minimal effort.

co-authored-by: Andreas Pelme <andreas@pelme.se>
co-authored-by: Simon Charette <charette.s@gmail.com>
co-authored-by: Jacob Walls <jacobtylerwalls@gmail.com>

1 files changed, 42 insertions, 1 deletions

diff --git a/tests/generic_relations/tests.py b/tests/generic_relations/tests.py
index 1b53dbd8f4..3de243d7b8 100644
--- a/tests/generic_relations/tests.py
+++ b/tests/generic_relations/tests.py
@@ -1,7 +1,8 @@
 from django.contrib.contenttypes.models import ContentType
 from django.contrib.contenttypes.prefetch import GenericPrefetch
-from django.core.exceptions import FieldError
+from django.core.exceptions import FieldError, FieldFetchBlocked
 from django.db.models import Q, prefetch_related_objects
+from django.db.models.fetch_modes import FETCH_PEERS, RAISE
 from django.test import SimpleTestCase, TestCase, skipUnlessDBFeature
 
 from .models import (
@@ -780,6 +781,46 @@ class GenericRelationsTests(TestCase):
                 self.platypus.latin_name,
             )
 
+    def test_fetch_mode_fetch_peers(self):
+        TaggedItem.objects.bulk_create(
+            [
+                TaggedItem(tag="lion", content_object=self.lion),
+                TaggedItem(tag="platypus", content_object=self.platypus),
+                TaggedItem(tag="quartz", content_object=self.quartz),
+            ]
+        )
+        # Peers fetching should fetch all related peers GFKs at once which is
+        # one query per content type.
+        with self.assertNumQueries(1):
+            quartz_tag, platypus_tag, lion_tag = TaggedItem.objects.fetch_mode(
+                FETCH_PEERS
+            ).order_by("-pk")[:3]
+        with self.assertNumQueries(2):
+            self.assertEqual(lion_tag.content_object, self.lion)
+        with self.assertNumQueries(0):
+            self.assertEqual(platypus_tag.content_object, self.platypus)
+            self.assertEqual(quartz_tag.content_object, self.quartz)
+        # It should ignore already cached instances though.
+        with self.assertNumQueries(1):
+            quartz_tag, platypus_tag, lion_tag = TaggedItem.objects.fetch_mode(
+                FETCH_PEERS
+            ).order_by("-pk")[:3]
+        with self.assertNumQueries(2):
+            self.assertEqual(quartz_tag.content_object, self.quartz)
+            self.assertEqual(lion_tag.content_object, self.lion)
+        with self.assertNumQueries(0):
+            self.assertEqual(platypus_tag.content_object, self.platypus)
+            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:
+            tag.content_object
+        self.assertIsNone(cm.exception.__cause__)
+        self.assertTrue(cm.exception.__suppress_context__)
+
 
 class ProxyRelatedModelTest(TestCase):
     def test_default_behavior(self):