Refs #28834 -- Moved ancestor field cached value fallback to related fields descriptor.

django/db/models/fields/mixins.py

@@ -12,22 +12,6 @@ class FieldCacheMixin:
         try:
             return instance._state.fields_cache[cache_name]
         except KeyError:
-            # An ancestor link will exist if this field is defined on a
-            # multi-table inheritance parent of the instance's class.
-            ancestor_link = instance._meta.get_ancestor_link(self.model)
-            if ancestor_link:
-                try:
-                    # The value might be cached on an ancestor if the instance
-                    # originated from walking down the inheritance chain.
-                    ancestor = ancestor_link.get_cached_value(instance)
-                except KeyError:
-                    pass
-                else:
-                    value = self.get_cached_value(ancestor)
-                    # Cache the ancestor value locally to speed up future
-                    # lookups.
-                    self.set_cached_value(instance, value)
-                    return value
             if default is NOT_PROVIDED:
                 raise
             return default

django/db/models/fields/related_descriptors.py

@@ -162,10 +162,18 @@ class ForwardManyToOneDescriptor:
         try:
             rel_obj = self.field.get_cached_value(instance)
         except KeyError:
-            val = self.field.get_local_related_value(instance)
+            has_value = None not in self.field.get_local_related_value(instance)
-            if None in val:
+            ancestor_link = instance._meta.get_ancestor_link(self.field.model) if has_value else None
-                rel_obj = None
+            if ancestor_link and ancestor_link.is_cached(instance):
+                # An ancestor link will exist if this field is defined on a
+                # multi-table inheritance parent of the instance's class.
+                ancestor = ancestor_link.get_cached_value(instance)
+                # The value might be cached on an ancestor if the instance
+                # originated from walking down the inheritance chain.
+                rel_obj = self.field.get_cached_value(ancestor, default=None)
             else:
+                rel_obj = None
+            if rel_obj is None and has_value:
                 rel_obj = self.get_object(instance)
                 remote_field = self.field.remote_field
                 # If this is a one-to-one relation, set the reverse accessor