private IQueryable <IdentityUser> FilterUsers(IQueryable <IdentityUser> query, UserFilter filter)
        {
            if (filter != null)
            {
                query = filter.Filter(query);
            }

            return(query);
        }
        public async Task <IEnumerable <UserModel> > GetAllWithFilter(UserFilter filter)
        {
            IEnumerable <UserModel> UserList = await queryIdentityUser(this.FilterUsers(db.Users, filter)).ToListAsync();

            return(UserList);
        }