Entity Framework无法更新数据。获取数据是正常的,该怎么解决

    public class EFProductRepository : IProductRepository    {        private EFDbContext context = new EFDbContext();        public IQueryable<Product> Products         {            get { return context.Products; }        }        public void SaveProduct(Product product)        {            if (product.ProductID == 0)            {                context.Products.Add(product);            }            context.SaveChanges();        }    }        [HttpPost]        public ActionResult Edit(Product product)        {            if (ModelState.IsValid)            {                repository.SaveProduct(product);                TempData["Message"] = string.Format("{0} have been saving.", product.Name);                return RedirectToAction("Index");            }            else            {                return View(product);            }        }