Add patterns for joining tables in API list methods

i.e. we needed to do an *outer* join on User.person since that can be null

tailbone/api/users.py

@@ -43,16 +43,20 @@ class UserView(APIMasterView):
     def normalize(self, user):
         return {
             'username': user.username,
-            'person_name': six.text_type(user.person or ''),
+            'person_display_name': (user.person.display_name or '') if user.person else '',
             'active': user.active,
         }
 
     def interpret_sortcol(self, order_by):
-        if order_by == 'person_name':
-            return self.sortcol('display_name', 'Person')
-
+        if order_by == 'person_display_name':
+            return self.sortcol('Person', 'display_name')
         return self.sortcol(order_by)
 
+    def join_for_sort_model(self, query, model_name):
+        if model_name == 'Person':
+            query = query.outerjoin(model.Person)
+        return query
+
     @view(permission='users.list')
     def collection_get(self):
         return self._collection_get()