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);
            }
        }