Fixed #36295, Refs #24305 -- Allowed overriding GenericForeignKey fields on abstract models.

AUTHORS

@@ -34,6 +34,7 @@ answer newbie questions, and generally made Django that much better:
     Ahmad Alhashemi <trans@ahmadh.com>
     Ahmad Al-Ibrahim
     Ahmed Eltawela <https://github.com/ahmedabt>
+    Ahmed Nassar <https://ahmednassar7.github.io/>
     ajs <adi@sieker.info>
     Akash Agrawal <akashrocksha@gmail.com>
     Akash Kumar Sen <akashkumarsen4@gmail.com>

django/db/models/base.py

@@ -348,7 +348,7 @@ class ModelBase(type):
                 new_class._meta.parents.update(base_parents)
 
             # Inherit private fields (like GenericForeignKey) from the parent
-            # class
+            # class if they are not overridden.
             for field in base._meta.private_fields:
                 if field.name in field_names:
                     if not base._meta.abstract:
@@ -361,7 +361,10 @@ class ModelBase(type):
                                 base.__name__,
                             )
                         )
-                else:
+                elif (
+                    field.name not in new_class.__dict__
+                    and field.name not in inherited_attributes
+                ):
                     field = copy.deepcopy(field)
                     if not base._meta.abstract:
                         field.mti_inherited = True

tests/model_inheritance/test_abstract_inheritance.py

@@ -184,6 +184,32 @@ class AbstractInheritanceTests(SimpleTestCase):
             ExtendModelAbstract._meta.get_field("field"), GenericRelation
         )
 
+    def test_override_private_field_with_attr(self):
+        class AbstractBase(models.Model):
+            content_type = models.ForeignKey(
+                ContentType, on_delete=models.SET_NULL, null=True, blank=True
+            )
+            object_id = models.PositiveIntegerField(null=True, blank=True)
+            related_object = GenericForeignKey("content_type", "object_id")
+
+            class Meta:
+                abstract = True
+
+        class Descendant(AbstractBase):
+            related_object = None
+
+        class Mixin:
+            related_object = None
+
+        class MultiDescendant(Mixin, AbstractBase):
+            pass
+
+        with self.assertRaises(FieldDoesNotExist):
+            Descendant._meta.get_field("related_object")
+
+        with self.assertRaises(FieldDoesNotExist):
+            MultiDescendant._meta.get_field("related_object")
+
     def test_cannot_override_indirect_abstract_field(self):
         class AbstractBase(models.Model):
             name = models.CharField(max_length=30)