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

django/core/serializers/base.py

@@ -88,7 +88,7 @@ class Serializer(object):
                         if self.selected_fields is None or field.attname in self.selected_fields:
                             self.handle_field(obj, field)
                     else:
-                        if self.selected_fields is None or field.attname[:-3] in self.selected_fields:
+                        if self.field_is_selected(field) and self.output_pk_field(obj, field):
                             self.handle_fk_field(obj, field)
             for field in concrete_model._meta.many_to_many:
                 if field.serialize:
@@ -101,6 +101,12 @@ class Serializer(object):
         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

@@ -13,6 +13,7 @@ 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.utils import six
 from django.utils.datastructures import ImmutableList, OrderedSet
 from django.utils.deprecation import (
@@ -296,7 +297,11 @@ class Options(object):
     def setup_pk(self, field):
         if not self.pk and field.primary_key:
             self.pk = field
-            field.serialize = False
+            # 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
 
     def setup_proxy(self, target):
         """