我的代码有问题。我收到此错误消息“值不能为空。参数名称：源”
下面是错误行100.
CartId和ShoppingCartId是字符串。
Rad 98: public List<Cart> GetCartItems()
Rad 99: {
Rad 100: return storeDB.Carts.Where(cart => cart.CartId == ShoppingCartId).ToList();
Rad 101: }
Rad 102:
[ArgumentNullException：Value不能为null。
Parameternamn：来源]
System.Linq.Queryable.Where（IQueryable 1 source, Expression 1谓词）+2713614
public class Cart
{
[Key]
public int RecordId { get; set; }
public String CartId { get; set; }
public int ProductId { get; set; }
public int Count { get; set; }
public System.DateTime DateCreated { get; set; }
public virtual Produkt Product { get; set; }
}
}
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.Data.Entity;
using System.Data.Objects;
namespace Test123.Models
{
public class ShoppingCart
{
Test123Entities storeDB = new Test123Entities();
string ShoppingCartId { get; set; }
public const string CartSessionKey = "CartId";
public static ShoppingCart GetCart(HttpContextBase context)
{
var cart = new ShoppingCart();
cart.ShoppingCartId = cart.GetCartId(context);
return cart;
}
// Helper method to simplify shopping cart calls
public static ShoppingCart GetCart(Controller controller)
{
return GetCart(controller.HttpContext);
}
public void AddToCart(Produkt product)
{
// Get the matching cart and product instances
var cartItem = storeDB.Carts.SingleOrDefault(
c => c.CartId == ShoppingCartId
&& c.ProductId == product.Produkt1);
if (cartItem == null)
{
// Create a new cart item if no cart item exists
cartItem = new Cart
{
ProductId = product.Produkt1,
CartId = ShoppingCartId,
Count = 1,
DateCreated = DateTime.Now
};
storeDB.Carts.Add(cartItem);
}
else
{
// If the item does exist in the cart,
// then add one to the quantity
cartItem.Count++;
}
// Save changes
//storeDB.Savechanges();
}
public int RemoveFromCart(int id)
{
// Get the cart
var cartItem = storeDB.Carts.Single(
cart => cart.CartId == ShoppingCartId
&& cart.RecordId == id);
int itemCount = 0;
if (cartItem != null)
{
if (cartItem.Count > 1)
{
cartItem.Count--;
itemCount = cartItem.Count;
}
else
{
storeDB.Carts.Remove(cartItem);
}
// Save changes
// storeDB.SaveChanges();
}
return itemCount;
}
public void EmptyCart()
{
var cartItems = storeDB.Carts.Where(
cart => cart.CartId == ShoppingCartId);
foreach (var cartItem in cartItems)
{
storeDB.Carts.Remove(cartItem);
}
// Save changes
// storeDB.SaveChanges();
}
public List<Cart> GetCartItems()
{
return storeDB.Carts.Where(cart => cart.CartId == ShoppingCartId).ToList();
}
public int GetCount()
{
// Get the count of each item in the cart and sum them up
int? count = (from cartItems in storeDB.Carts
where cartItems.CartId == ShoppingCartId
select (int?)cartItems.Count).Sum();
// Return 0 if all entries are null
return count ?? 0;
}
public decimal GetTotal()
{
// Multiply product price by count of that product to get
// the current price for each of those products in the cart
// sum all product price totals to get the cart total
decimal? total = (from cartItems in storeDB.Carts
where cartItems.CartId == ShoppingCartId
select (int?)cartItems.Count *
cartItems.Product.Pris).Sum();
return total ?? decimal.Zero;
}
public int CreateOrder(Order order)
{
decimal orderTotal = 0;
var cartItems = GetCartItems();
// Iterate over the items in the cart,
// adding the order details for each
foreach (var item in cartItems)
{
var orderDetail = new OrderDetail
{
ProductId = item.ProductId,
OrderId = order.OrderId,
UnitPrice = item.Product.Pris,
Quantity = item.Count
};
// Set the order total of the shopping cart
orderTotal += (item.Count * item.Product.Pris);
storeDB.OrderDetails.Add(orderDetail);
}
// Set the order's total to the orderTotal count
order.Total = orderTotal;
// Save the order
storeDB.Orders.Add(order);
// storeDB.SaveChanges();
// Empty the shopping cart
EmptyCart();
// Return the OrderId as the confirmation number
return order.OrderId;
}
// We're using HttpContextBase to allow access to cookies.
public string GetCartId(HttpContextBase context)
{
if (context.Session[CartSessionKey] == null)
{
if (!string.IsNullOrWhiteSpace(context.User.Identity.Name))
{
context.Session[CartSessionKey] =
context.User.Identity.Name;
}
else
{
// Generate a new random GUID using System.Guid class
Guid tempCartId = Guid.NewGuid();
// Send tempCartId back to client as a cookie
context.Session[CartSessionKey] = tempCartId.ToString();
}
}
return context.Session[CartSessionKey].ToString();
}
}
}
控制器
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using Test123.Models;
using Test123.ViewModel;
namespace Test123.Controllers
{
// GET: ShoppingCart
public class ShoppingCartController : Controller
{
Test123Entities storeDB = new Test123Entities();
// GET: /ShoppingCart/
public ActionResult Index()
{
var cart = ShoppingCart.GetCart(this.HttpContext);
// Set up our ViewModel
var viewModel = new ShoppingCartViewModel
{
CartItems = cart.GetCartItems(),
CartTotal = cart.GetTotal()
};
return View(viewModel);
}
// GET: /Store/AddToCart/5
public ActionResult AddToCart(int id)
{
// Retrieve the product from the database
var addedProduct = storeDB.Products
.Single(product => product.Produkt1 == id);
// Add it to the shopping cart
var cart = ShoppingCart.GetCart(this.HttpContext);
cart.AddToCart(addedProduct);
// Go back to the main store page for more shopping
return RedirectToAction("Index");
}
// AJAX: /ShoppingCart/RemoveFromCart/5
[HttpPost]
public ActionResult RemoveFromCart(int id)
{
// Remove the item from the cart
var cart = ShoppingCart.GetCart(this.HttpContext);
// Get the name of the product to display confirmation
string productName = storeDB.Carts
.Single(item => item.RecordId == id).Product.Namn;
// Remove from cart
int itemCount = cart.RemoveFromCart(id);
// Display the confirmation message
var results = new ShoppingCartRemoveViewModel
{
Message = Server.HtmlEncode(productName) +
" el lett távolítva a bevásárlókosárból.",
CartTotal = cart.GetTotal(),
CartCount = cart.GetCount(),
ItemCount = itemCount,
DeleteId = id
};
return Json(results);
}
// GET: /ShoppingCart/CartSummary
[ChildActionOnly]
public ActionResult CartSummary()
{
var cart = ShoppingCart.GetCart(this.HttpContext);
ViewData["CartCount"] = cart.GetCount();
return PartialView("CartSummary");
}
}
}
购物车的抄袭
public class Test123Entities
{
public DbSet<Cart> Carts { get; set; }
public DbSet<Produkt> Products { get; set; }
public DbSet<Order> Orders { get; set; }
public DbSet<OrderDetail> OrderDetails { get; set; }
public DbSet<Kategori> Categories { get; set; }
}
}
答案 0 :(得分：1)
添加空检查
public List<Cart> GetCartItems()
{
if(storeDB.Carts != null)
{
return storeDB.Carts
.Where(cart => cart.CartId == ShoppingCartId)
.ToList();
}
return new List<Cart>();
}
采用引用类型的 System.Linq 中的每个方法都将检查它们是否为空if(source== null)并抛出ArgumentNullException（如果它们）。
在这种情况下，您调用的Where是IEnumerable<TSource>的扩展方法。 Where
public static IEnumerable<TSource> Where<TSource>(this IEnumerable<TSource> source, Func<TSource, int, bool> predicate);
public static IEnumerable<TSource> Where<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate);
如您所见，第一个参数名称为＆＃34; source＆＃34;，错误为：
值不能为空。参数名称：source
这意味着Carts是null。添加null检查将解决问题