Question

我一直在遵循有关如何使用.net核心为网站添加购物车功能的教程，但是当我单击“添加到购物车”按钮时，它为我的操作方法提供了空值。 Add to cart returns a null value

这里应该是什么错误？

这是我的控制器类

namespace SanMarinoClassicWebsite.Controllers
{
    public class ShoppingCartController : Controller
    {
        private readonly IPieRepository _pieRepository;
        private readonly ShoppingCart _shoppingCart;

        public ShoppingCartController(IPieRepository pieRepository, ShoppingCart shoppingCart)
        {
            _pieRepository = pieRepository;
            _shoppingCart = shoppingCart;
        }

        public ViewResult Index()
        {
            var items = _shoppingCart.GetShoppingCartItems();
            _shoppingCart.ShoppingCartItems = items;

            var shoppingCartViewModel = new ShoppingCartViewModel
            {
                ShoppingCart = _shoppingCart,
                ShoppingCartTotal = _shoppingCart.GetShoppingCartTotal()
            };

            return View(shoppingCartViewModel);
        }
         public RedirectToActionResult AddToShoppingCart(int pieId)
        {
            var selectedPie = _pieRepository.Pies.FirstOrDefault(p => p.PieId == pieId);

            if (selectedPie != null)
            {
                _shoppingCart.AddToCart(selectedPie, 1);
            }
            return RedirectToAction("Index");
        }

        public RedirectToActionResult RemoveFromShoppingCart(int pieId)
        {
            var selectedPie = _pieRepository.Pies.FirstOrDefault(p => p.PieId == pieId);

            if (selectedPie != null)
            {
                _shoppingCart.RemoveFromCart(selectedPie);
            }
            return RedirectToAction("Index");
        }
    }
}

购物车模型

namespace SanMarinoClassicWebsite.Models
{
    public class ShoppingCart
    {
        private readonly AppDbContext _appDbContext;
        private ShoppingCart(AppDbContext appDbContext)
        {
            _appDbContext = appDbContext;
        }

        public string ShoppingCartId { get; set; }

        public List<ShoppingCartItem> ShoppingCartItems { get; set; }

        public static ShoppingCart GetCart(IServiceProvider services)
        {
            ISession session = services.GetRequiredService<IHttpContextAccessor>()?
                .HttpContext.Session;

            var context = services.GetService<AppDbContext>();
            string cartId = session.GetString("CartId") ?? Guid.NewGuid().ToString();

            session.SetString("CartId", cartId);

            return new ShoppingCart(context) { ShoppingCartId = cartId };
        }

        public void AddToCart(Pie pie, int amount)
        {
            var shoppingCartItem =
                    _appDbContext.ShoppingCartItems.SingleOrDefault(
                        s => s.Pie.PieId == pie.PieId && s.ShoppingCartId == ShoppingCartId);

            if (shoppingCartItem == null)
            {
                shoppingCartItem = new ShoppingCartItem
                {
                    ShoppingCartId = ShoppingCartId,
                    Pie = pie,
                    Amount = 1
                };

                _appDbContext.ShoppingCartItems.Add(shoppingCartItem);
            }
            else
            {
                shoppingCartItem.Amount++;
            }
            _appDbContext.SaveChanges();
        }

        public int RemoveFromCart(Pie pie)
        {
            var shoppingCartItem =
                    _appDbContext.ShoppingCartItems.SingleOrDefault(
                        s => s.Pie.PieId == pie.PieId && s.ShoppingCartId == ShoppingCartId);

            var localAmount = 0;

            if (shoppingCartItem != null)
            {
                if (shoppingCartItem.Amount > 1)
                {
                    shoppingCartItem.Amount--;
                    localAmount = shoppingCartItem.Amount;
                }
                else
                {
                    _appDbContext.ShoppingCartItems.Remove(shoppingCartItem);
                }
            }

            _appDbContext.SaveChanges();

            return localAmount;
        }

        public List<ShoppingCartItem> GetShoppingCartItems()
        {
            return ShoppingCartItems ??
                   (ShoppingCartItems =
                       _appDbContext.ShoppingCartItems.Where(c => c.ShoppingCartId == ShoppingCartId)
                           .Include(s => s.Pie)
                           .ToList());
        }

        public void ClearCart()
        {
            var cartItems = _appDbContext
                .ShoppingCartItems
                .Where(cart => cart.ShoppingCartId == ShoppingCartId);

            _appDbContext.ShoppingCartItems.RemoveRange(cartItems);

            _appDbContext.SaveChanges();
        }



        public decimal GetShoppingCartTotal()
        {
            var total = _appDbContext.ShoppingCartItems.Where(c => c.ShoppingCartId == ShoppingCartId)
                .Select(c => c.Pie.Price * c.Amount).Sum();
            return total;
        }
    }
}

Startup.cs 公共类创业 { 私人IConfigurationRoot _configurationRoot;

    public Startup(IHostingEnvironment hostingEnvironment)
    {
        _configurationRoot = new ConfigurationBuilder()
               .SetBasePath(hostingEnvironment.ContentRootPath)
               .AddJsonFile("appsettings.json")
               .Build(); 

    }

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddDbContext<AppDbContext>(options =>
                                options.UseSqlServer(_configurationRoot.GetConnectionString("DefaultConnection")));
        services.AddTransient<ICategoryRepository, CategoryRepository>();
        services.AddTransient<IPieRepository, PieRepository>();
        services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
        services.AddScoped<ShoppingCart>(sp => ShoppingCart.GetCart(sp));

        services.AddMvc();
        services.AddMemoryCache();
        services.AddSession();
    }


    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        app.UseDeveloperExceptionPage();
        app.UseStatusCodePages();
        app.UseStaticFiles();
        app.UseSession();

        app.UseMvc(routes =>
        {
            routes.MapRoute(
                name: "categoryfilter",
                template:"Pie/{action}/{category?}",
                defaults: new {Controller ="Pie", action ="List"});

            routes.MapRoute(
                name: "default",
                template: "{controller=Home}/{action=Index}/{id?}");
        });


    }
}

}

Answer 1

我发现了我的错误，似乎我错误地使用了asp-route标签助手。我使用了asp-route-id而不是asp-route-pieId，

这些是片段

<a class="btn btn-primary" asp-controller="ShoppingCart" asp-action="AddToShoppingCart" asp-route-id="@Model.PieId">

<a class="btn btn-primary" asp-controller="ShoppingCart" asp-action="AddToShoppingCart" asp-route-pieId="@Model.PieId">

添加到购物车函数返回空值

1 个答案: