public ActionResult DetailsEdit(int id)
        {
            CustomerDetailsViewModel model;

            //# validation
            if (id < 0)
                throw new SystemException("Invalid Entity ID");

            model = new CustomerDetailsViewModel()
            {
                id = id,
                Mode = PageMode.Edit
            };

            return View("Details", model);
        }
        public ActionResult DetailsAdd()
        {
            CustomerDetailsViewModel model;

            model = new CustomerDetailsViewModel()
            {
                Mode = PageMode.Add
            };

            return View("Details", model);
        }