public static string Restore(SiteSettings ss, int groupId)
        {
            var groupModel = new GroupModel();
            var invalid    = GroupValidators.OnRestoring();

            switch (invalid)
            {
            case Error.Types.None: break;

            default: return(invalid.MessageJson());
            }
            var error = groupModel.Restore(ss, groupId);

            if (error.Has())
            {
                return(error.MessageJson());
            }
            else
            {
                var res = new GroupsResponseCollection(groupModel);
                return(res.ToJson());
            }
        }