Fixed #22421 -- Regression in fixtures loading.

Loading fixtures were failing since the refactoring in 244e2b71f5 for
inheritance setups where the chain contains abstract models and the
root ancestor contains a M2M relation.

Thanks Stanislas Guerra for the report.

Refs #20946.

1 files changed, 4 insertions, 2 deletions

diff --git a/django/db/models/fields/related.py b/django/db/models/fields/related.py
index bad457f571..ceae2cd563 100644
--- a/django/db/models/fields/related.py
+++ b/django/db/models/fields/related.py
@@ -1440,14 +1440,16 @@ class ForeignObject(RelatedField):
     @staticmethod
     def get_instance_value_for_fields(instance, fields):
         ret = []
+        opts = instance._meta
         for field in fields:
             # Gotcha: in some cases (like fixture loading) a model can have
             # different values in parent_ptr_id and parent's id. So, use
             # instance.pk (that is, parent_ptr_id) when asked for instance.id.
-            opts = instance._meta
             if field.primary_key:
                 possible_parent_link = opts.get_ancestor_link(field.model)
-                if not possible_parent_link or possible_parent_link.primary_key:
+                if (not possible_parent_link or
+                        possible_parent_link.primary_key or
+                        possible_parent_link.model._meta.abstract):
                     ret.append(instance.pk)
                     continue
             ret.append(getattr(instance, field.attname))