public HttpResponseMessage DeleteEmployee(string employee_id)
        {
            HttpResponseMessage response = new HttpResponseMessage();

            try
            {
                ManagementHelper.DeleteEmployee(employee_id);
            }
            catch (Exception e)
            {
                response.Content    = new StringContent(e.Message);
                response.StatusCode = HttpStatusCode.BadRequest;
            }
            response.Content = new StringContent("更新成功!");
            return(response);
        }