Question

我使用音乐商店购物车代码为我的mvc项目，但我的项目使用linq到sql，而不是实体框架。我已将MusicStoreEntities类更改为：

public class ShoppingCartEntities
{
    public ShoppingCartEntities()
    {
    }
    public List<h2t_Store_Product> Products { get; set; }
    public List<Cart> Carts { get; set; }
    public List<Order> Orders { get; set; }
    public List<OrderDetail> OrderDetails { get; set; }
}

这些是ShoppingCart.cs类：

public class ShoppingCart
{
    ShoppingCartEntities storeDB = new ShoppingCartEntities();
    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(h2t_Store_Product product)
    {
        // Get the matching cart and album instances
        var cartItem = (from data in storeDB.Carts
                        where data.CartId == ShoppingCartId && data.ProductID == product.ID
                        select data).Single();

        if (cartItem == null)
        {
            // Create a new cart item if no cart item exists
            cartItem = new Cart
            {
                ProductID = product.ID,
                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 album price by count of that album to get 
        // the current price for each of those albums in the cart
        // sum all album price totals to get the cart total
        decimal? total = (from cartItems in storeDB.Carts
                          where cartItems.CartId == ShoppingCartId
                          select (int?)cartItems.Count *
                          cartItems.product.UnitPrice).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
            {
                AlbumId = item.ProductID,
                OrderId = order.OrderId,
                UnitPrice = item.product.UnitPrice,
                Quantity = item.Count
            };
            // Set the order total of the shopping cart
            orderTotal += (item.Count * item.product.UnitPrice);

            storeDB.OrderDetails.Add(orderDetail);

        }
        // Set the order's total to the orderTotal count
        order.Total = orderTotal;

        // Save the 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();
    }
    // When a user has logged in, migrate their shopping cart to
    // be associated with their username
    public void MigrateCart(string userName)
    {
        var shoppingCart = storeDB.Carts.Where(
            c => c.CartId == ShoppingCartId);

        foreach (Cart item in shoppingCart)
        {
            item.CartId = userName;
        }
        //storeDB.SaveChanges();
    }
}

Anh Cart.cs课程：

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 h2t_Store_Product product { get; set; }

}

当我运行项目时，我收到错误：

值不能为空。参数名称：source

enter image description here

任何人都可以告诉我如何解决它？非常感谢你。

Answer 1

这不会作为linq-to-sql运行，而是作为linq-to-objects运行。 linq查询的来源为ShoppingCartEntities.Carts，即List<Cart>。

异常消息表示执行查询时Carts为null。我无法看到您在提供的代码中的任何位置对该列表进行了实例化。

如果您尝试将此转换为EF Code First示例，则很容易错过该步骤。当使用EF Code First时，实体集会自动从基类中获取值（可通过反射推测），但linq-to-sql中不存在“魔法”。

Mvc音乐商店linq到sql购物车

1 个答案: