[1.4.x] Fixed #23329 -- Allowed inherited and m2m fields to be referenced in the admin.

Thanks to Trac alias Markush2010 and ross for the detailed reports.

Backport of 3cbb759 from master

1 files changed, 6 insertions, 4 deletions

diff --git a/django/contrib/admin/options.py b/django/contrib/admin/options.py
index cf3497b93c..fa7a6f0b9c 100644
--- a/django/contrib/admin/options.py
+++ b/django/contrib/admin/options.py
@@ -278,11 +278,13 @@ class BaseModelAdmin(object):
             return False
 
         # Make sure at least one of the models registered for this site
-        # references this field.
+        # references this field through a FK or a M2M relationship.
         registered_models = self.admin_site._registry
-        for related_object in opts.get_all_related_objects():
-            if (related_object.model in registered_models and
-                    field == related_object.field.rel.get_related_field()):
+        for related_object in (opts.get_all_related_objects() +
+                               opts.get_all_related_many_to_many_objects()):
+            related_model = related_object.model
+            if (any(issubclass(model, related_model) for model in registered_models) and
+                    related_object.field.rel.get_related_field() == field):
                 return True
 
         return False