public ActionResult Create(ProductAttribute model)
        {
            try
            {
                using (var context = new ShopContainer())
                {
                    if (string.IsNullOrEmpty(model.ValueType))
                        model.ValueType = string.Empty;
                    context.AddToProductAttribute(model);
                    context.SaveChanges();
                }

                return RedirectToAction("Index");
            }
            catch
            {
                return View();
            }
        }