Fixed #27742 -- Reverted "Fixed #24607 -- Serialized natural keys in multi-table inheritance models."

This reverts commit 74a575eb7296fb04e1fc2bd4e3f68dee3c66ee0a as it causes
unexpected migrations and doesn't seem to be the best solution.

django/core/serializers/base.py

@@ -88,7 +88,7 @@ class Serializer:
                         if self.selected_fields is None or field.attname in self.selected_fields:
                             self.handle_field(obj, field)
                     else:
-                        if self.field_is_selected(field) and self.output_pk_field(obj, field):
+                        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:
                 if field.serialize:
@@ -101,12 +101,6 @@ class Serializer:
         self.end_serialization()
         return self.getvalue()
 
-    def field_is_selected(self, field):
-        return self.selected_fields is None or field.attname[:-3] in self.selected_fields
-
-    def output_pk_field(self, obj, pk_field):
-        return self.use_natural_primary_keys or pk_field != obj._meta.pk
-
     def start_serialization(self):
         """
         Called when serializing of the queryset starts.

django/db/models/options.py

@@ -11,7 +11,6 @@ from django.db import connections
 from django.db.models import Manager
 from django.db.models.fields import AutoField
 from django.db.models.fields.proxy import OrderWrt
-from django.db.models.fields.related import OneToOneField
 from django.db.models.query_utils import PathInfo
 from django.utils.datastructures import ImmutableList, OrderedSet
 from django.utils.deprecation import RemovedInDjango21Warning
@@ -281,11 +280,7 @@ class Options:
     def setup_pk(self, field):
         if not self.pk and field.primary_key:
             self.pk = field
-            # If the field is a OneToOneField and it's been marked as PK, then
-            # this is a multi-table inheritance PK. It needs to be serialized
-            # to relate the subclass instance to the superclass instance.
-            if not isinstance(field, OneToOneField):
-                field.serialize = False
+            field.serialize = False
 
     def setup_proxy(self, target):
         """

tests/serializers/models/__init__.py

@@ -1,4 +1,3 @@
 from .base import *  # NOQA
 from .data import *  # NOQA
-from .multi_table import *  # NOQA
 from .natural import *  # NOQA

tests/serializers/models/multi_table.py

@@ -1,19 +0,0 @@
-from django.db import models
-
-
-class ParentManager(models.Manager):
-    def get_by_natural_key(self, parent_data):
-        return self.get(parent_data=parent_data)
-
-
-class Parent(models.Model):
-    parent_data = models.CharField(max_length=30, unique=True)
-
-    objects = ParentManager()
-
-    def natural_key(self):
-        return (self.parent_data, )
-
-
-class Child(Parent):
-    child_data = models.CharField(max_length=30, unique=True)

tests/serializers/test_natural.py

@@ -2,7 +2,7 @@ from django.core import serializers
 from django.db import connection
 from django.test import TestCase
 
-from .models import Child, FKDataNaturalKey, NaturalKeyAnchor
+from .models import FKDataNaturalKey, NaturalKeyAnchor
 from .tests import register_tests
 
 
@@ -67,37 +67,6 @@ def natural_key_test(format, self):
     self.assertIsNone(books[1].object.pk)
 
 
-def natural_pk_mti_test(format, self):
-    """
-    If serializing objects in a multi-table inheritance relationship using
-    natural primary keys, the natural foreign key for the parent is output in
-    the fields of the child so it's possible to relate the child to the parent
-    when deserializing.
-    """
-    child_1 = Child.objects.create(parent_data='1', child_data='1')
-    child_2 = Child.objects.create(parent_data='2', child_data='2')
-
-    string_data = serializers.serialize(
-        format,
-        [child_1.parent_ptr, child_2.parent_ptr, child_2, child_1],
-        use_natural_foreign_keys=True, use_natural_primary_keys=True,
-    )
-
-    child_1.delete()
-    child_2.delete()
-
-    for obj in serializers.deserialize(format, string_data):
-        obj.save()
-
-    children = Child.objects.all()
-    self.assertEqual(len(children), 2)
-    for child in children:
-        # If it's possible to find the superclass from the subclass and it's
-        # the correct superclass, it's working.
-        self.assertEqual(child.child_data, child.parent_data)
-
-
 # Dynamically register tests for each serializer
 register_tests(NaturalKeySerializerTests, 'test_%s_natural_key_serializer', natural_key_serializer_test)
 register_tests(NaturalKeySerializerTests, 'test_%s_serializer_natural_keys', natural_key_test)
-register_tests(NaturalKeySerializerTests, 'test_%s_serializer_natural_pks_mti', natural_pk_mti_test)