public ActionResult Edit(Product product)
 {
     if (ModelState.IsValid)
     {
         db.Entry(product).State = EntityState.Modified;
         db.SaveChanges();
         return(RedirectToAction("Index"));
     }
     ViewBag.CategoryID = new SelectList(db.Categories, "CategoryID", "CategoryName", product.CategoryID);
     return(View(product));
 }