public ActionResult AddComment(int id)
        {
            var user = _db.Users.FirstOrDefault(x => x.UserName.Equals(User.Identity.Name));
            if (user != null && user.Reviews.Any(x => x.Product.Id == id))
            {
                return RedirectToAction("ProductDetail", "ViewProduct", new { id });
            }

            var firstOrDefault = _db.Products.FirstOrDefault(x => x.Id == id);

            var productName = firstOrDefault.Name;

            var model = new CommentViewModel
            {
                ProductName = productName,
                Id = firstOrDefault.Id
            };

            return View(model);
        }
        public ActionResult AddComment(CommentViewModel model)
        {
            if (this.ModelState.IsValid)
            {
                var product = _db.Products.FirstOrDefault(x => x.Id == model.Id);
                var user = _db.Users.FirstOrDefault(x => x.UserName.Equals(User.Identity.Name));

                var rating = new Review
                {
                    AddDate = DateTime.Now,
                    Rating = model.Rating,
                    Comment = model.Comment,
                    Product = product,
                    User = user
                };

                _db.Reviews.Add(rating);
                _db.SaveChanges();
                return RedirectToAction("ProductDetail", "ViewProduct", new { model.Id });
            }
            return View();
        }