Fixed #28725 -- Prevented serializing inherited ManyToManyFields in child model.

django/core/serializers/base.py

@@ -108,7 +108,7 @@ class Serializer:
                     else:
                         if self.selected_fields is None or field.attname[:-3] in self.selected_fields:
                             self.handle_fk_field(obj, field)
-            for field in concrete_model._meta.many_to_many:
+            for field in concrete_model._meta.local_many_to_many:
                 if field.serialize:
                     if self.selected_fields is None or field.attname in self.selected_fields:
                         self.handle_m2m_field(obj, field)

tests/serializers/models/multi_table.py

@@ -8,6 +8,7 @@ class ParentManager(models.Manager):
 
 class Parent(models.Model):
     parent_data = models.CharField(max_length=30, unique=True)
+    parent_m2m = models.ManyToManyField('self')
 
     objects = ParentManager()
 

tests/serializers/tests.py

@@ -12,8 +12,9 @@ from django.test import SimpleTestCase, override_settings, skipUnlessDBFeature
 from django.test.utils import Approximate
 
 from .models import (
-    Actor, Article, Author, AuthorProfile, BaseModel, Category, ComplexModel,
-    Movie, Player, ProxyBaseModel, ProxyProxyBaseModel, Score, Team,
+    Actor, Article, Author, AuthorProfile, BaseModel, Category, Child,
+    ComplexModel, Movie, Player, ProxyBaseModel, ProxyProxyBaseModel, Score,
+    Team,
 )
 
 
@@ -340,6 +341,13 @@ class SerializersTestBase:
         self.assertEqual(base_data, proxy_data.replace('proxy', ''))
         self.assertEqual(base_data, proxy_proxy_data.replace('proxy', ''))
 
+    def test_serialize_inherited_m2m(self):
+        child_1 = Child.objects.create(parent_data='a', child_data='b')
+        child_2 = Child.objects.create(parent_data='c', child_data='d')
+        child_1.parent_m2m.add(child_2)
+        child_data = serializers.serialize(self.serializer_name, [child_1, child_2])
+        self.assertEqual(self._get_field_values(child_data, 'parent_m2m'), [])
+
 
 class SerializerAPITests(SimpleTestCase):