Check the new groups are different before update

Claimed groups can contain groups they are not relevant for our app
so the first quick check is to ensure the list are different then
to use a SQL query to fetch the groups of the user.
Only set the groups if they are different, it avoids a SELECT of
the Django ORM (called by the set()).

Author: stephane

django_auth_adfs/backend.py

@@ -382,6 +382,13 @@ def update_user_groups(self, user, claim_groups):
             if sorted(claim_groups) != sorted(user_group_names):
                 # Get the list of already existing groups in one SQL query
                 existing_claimed_groups = Group.objects.filter(name__in=claim_groups)
+                existing_claimed_group_names = (
+                    group.name for group in existing_claimed_groups
+                )
+
+                if sorted(existing_claimed_group_names) == sorted(user_group_names):
+                    # If the groups are already set, we don't need to do anything
+                    return
 
                 if settings.MIRROR_GROUPS:
                     existing_claimed_group_names = (