Added utility function to check if a model defined as a sortable foreign key inherits from Sortable and if there are more than one objects for that model.

adminsortable/utils.py

@@ -1,5 +1,17 @@
+from .models import Sortable
+
+
 def get_is_sortable(objects):
     if objects:
+        if issubclass(type(objects[0]), Sortable):
             if objects.count() > 1:
                 return True
     return False
+
+
+def check_model_is_sortable(cls):
+    if cls:
+        if issubclass(type(cls), Sortable):
+            if cls.objects.count() > 1:
+                return True
+    return False