Merge pull request #51 from dabapps/fix-reverse-m2m

For a reverse many-to-many relation we should not (cannot) prefetch the reverse FK
dabapps · Feb 21, 2020 · 2affb92 · 2affb92
2 parents 64ac3d1 + 6f06303
commit 2affb92
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Showing 3 changed files with 13 additions and 4 deletions.
diff --git a/serialization_spec/serialization.py b/serialization_spec/serialization.py
@@ -179,7 +179,9 @@ def prefetch_related(request_user, queryset, model, prefixes, serialization_spec
                                 for rel in model._meta.related_objects
                                 if rel.get_accessor_name() == key
                             )
-                            only_fields += ['%s_id' % reverse_fk]
+                            has_reverse_fk = any(field.name == reverse_fk for field in relation.related_model._meta.fields)
+                            if has_reverse_fk:
+                                only_fields += ['%s_id' % reverse_fk]
                         inner_queryset = prefetch_related(request_user, related_model.objects.only(*only_fields), related_model, [], childspec, use_select_related)
                         if filters:
                             inner_queryset = inner_queryset.filter(filters).distinct()

diff --git a/tests/tests.py b/tests/tests.py
@@ -130,15 +130,16 @@ def test_single_many_to_many(self):
             ],
         })
 
-    def test_single_fk_on_fk(self):
+    def test_single_fk_on_fk_and_reverse_m2m(self):
         with CaptureQueriesContext(connection) as capture:
             url = reverse('class-detail', kwargs={'id': str(self.math_class.id)})
             response = self.client.get(url)
 
         self.assertJsonEqual(
             sorted(query['sql'] for query in capture.captured_queries),
             [
-                """SELECT "tests_class"."id", "tests_class"."name", "tests_class"."teacher_id", "tests_teacher"."id", "tests_teacher"."created", "tests_teacher"."modified", "tests_teacher"."name", "tests_teacher"."school_id", "tests_school"."id", "tests_school"."created", "tests_school"."modified", "tests_school"."name", "tests_school"."lea_id" FROM "tests_class" INNER JOIN "tests_teacher" ON ("tests_class"."teacher_id" = "tests_teacher"."id") INNER JOIN "tests_school" ON ("tests_teacher"."school_id" = "tests_school"."id") WHERE "tests_class"."id" = '00000000-0000-0000-0000-000000000006'::uuid"""
+                """SELECT "tests_class"."id", "tests_class"."name", "tests_class"."teacher_id", "tests_teacher"."id", "tests_teacher"."created", "tests_teacher"."modified", "tests_teacher"."name", "tests_teacher"."school_id", "tests_school"."id", "tests_school"."created", "tests_school"."modified", "tests_school"."name", "tests_school"."lea_id" FROM "tests_class" INNER JOIN "tests_teacher" ON ("tests_class"."teacher_id" = "tests_teacher"."id") INNER JOIN "tests_school" ON ("tests_teacher"."school_id" = "tests_school"."id") WHERE "tests_class"."id" = '00000000-0000-0000-0000-000000000006'::uuid""",
+                """SELECT ("tests_student_classes"."class_id") AS "_prefetch_related_val_class_id", "tests_student"."id", "tests_student"."name" FROM "tests_student" INNER JOIN "tests_student_classes" ON ("tests_student"."id" = "tests_student_classes"."student_id") WHERE "tests_student_classes"."class_id" IN ('00000000-0000-0000-0000-000000000006'::uuid)"""
             ]
         )
 
@@ -153,6 +154,9 @@ def test_single_fk_on_fk(self):
                     "name": "Kitteh High"
                 },
             },
+            'student_set': [
+                {'name': 'Student 3'}, {'name': 'Student 4'}, {'name': 'Student 5'}, {'name': 'Student 6'}, {'name': 'Student 7'}, {'name': 'Student 8'}, {'name': 'Student 9'},
+            ]
         })
 
     def test_single_fk_on_many_to_many(self):

diff --git a/tests/views.py b/tests/views.py
@@ -72,7 +72,10 @@ class ClassDetailView(SerializationSpecMixin, generics.RetrieveAPIView):
                 'id',
                 'name'
             ]}
-        ]}
+        ]},
+        {'student_set': [
+            'name',
+        ]},
     ]