使用 EF 更新 PK 時出錯

Question

我正在嘗試使用 EF 4.1 (POCO) 在 Northwind 數據庫的 Order_Details 表中進行更新。 該表定義為：

[MetadataType(typeof(Order_DetailMetadata))]
public partial class Order_Detail
{
    public int OrderID { get; set; }
    public int ProductID { get; set; }
    public decimal UnitPrice { get; set; }
    public short Quantity { get; set; }
    public float Discount { get; set; }

    public virtual Order Order { get; set; }
    public virtual Product Product { get; set; }
}

public class Order_DetailMetadata
{
    [Key]
    [Required]
    [DisplayNameLocalized("Model_OrderDetail_OrderID_DisplayName")]
    public int OrderID { get; set; }

    [Key]
    [Required]
    [DisplayNameLocalized("Model_OrderDetail_ProductID_DisplayName")]
    public int ProductID { get; set; }

    [Required]
    [Range(0.00, 9999.99, ErrorMessageResourceType = typeof(Messages), ErrorMessageResourceName = "Model_Range_Float_Error")]
    [DisplayNameLocalized("Model_OrderDetail_UnitPrice_DisplayName")]
    public decimal UnitPrice { get; set; }

    [Required]
    [Range(1, short.MaxValue, ErrorMessageResourceType = typeof(Messages), ErrorMessageResourceName = "Model_Range_Integer_Error")]
    [DisplayNameLocalized("Model_OrderDetail_Quantity_DisplayName")]
    public short Quantity { get; set; }

    [Required]
    [DisplayNameLocalized("Model_OrderDetail_Discount_DisplayName")]
    [Range(0.00, 1.00, ErrorMessageResourceType = typeof(Messages), ErrorMessageResourceName = "Model_Range_Float_Error")]
    public float Discount { get; set; }
}

問題是，當我嘗試使用新產品更新 OrderDetail 項目時，出現異常：

The property 'ProductID' is part of the object's key information and cannot be modified.

代碼是：

        int orderId = (int)detailsList.DataKeys[e.ItemIndex]["OrderID"];
        int productId = (int)detailsList.DataKeys[e.ItemIndex]["ProductID"];

        Order_Detail detail = repository.GetOrderDetail(orderId, productId);
        detail.ProductID = int.Parse(e.NewValues["ProductID"] as string, CultureInfo.CurrentCulture);
        detail.UnitPrice = decimal.Parse(e.NewValues["UnitPrice"] as string, CultureInfo.CurrentCulture);
        detail.Quantity = short.Parse(e.NewValues["Quantity"] as string, CultureInfo.CurrentCulture);
        detail.Discount = float.Parse(e.NewValues["Discount"] as string, CultureInfo.CurrentCulture);

        repository.UpdateOrderDetail(detail);
        repository.Save();

我做了一些谷歌並找到了[this solution] ，說這樣做的一種方法是創建新產品的新實例並關聯到 Order_Detail 的產品導航屬性。

但這樣做我得到另一個例外：

A referential integrity constraint violation occurred: A primary key property that is a part of referential integrity constraint cannot be changed when the dependent object is Unchanged unless it is being set to the association's principal object. The principal object must be tracked and not marked for deletion.

修改后的代碼：

        int orderId = (int)detailsList.DataKeys[e.ItemIndex]["OrderID"];
        int productId = (int)detailsList.DataKeys[e.ItemIndex]["ProductID"];
        int newProductId = int.Parse(e.NewValues["ProductID"] as string, CultureInfo.CurrentCulture);

        Order_Detail detail = repository.GetOrderDetail(orderId, productId);

        detail.UnitPrice = decimal.Parse(e.NewValues["UnitPrice"] as string, CultureInfo.CurrentCulture);
        detail.Quantity = short.Parse(e.NewValues["Quantity"] as string, CultureInfo.CurrentCulture);
        detail.Discount = float.Parse(e.NewValues["Discount"] as string, CultureInfo.CurrentCulture);

        Product newProduct = null;
        // the product has been changed (it is part of the PK and cannot be directly changed)
        if (productId != newProductId)
        {
            // get an instance of the new product
            newProduct = repository.GetProduct(newProductId);
            // update the detail item with the new product instance
            detail.Product = newProduct;
        }

        repository.UpdateOrderDetail(detail);
        repository.Save();

我可以做些什么來允許用戶更改詳細信息項目中的產品？ 我真的不喜歡刪除整個記錄並使用新產品重新創建它的想法。 它聞起來很糟糕！

謝謝！

Answer 1

桌子設計得很差。 實際上，您將不得不刪除並重新添加整行。

正確的設計應該有一個單獨的列作為 Order Details 表的主鍵（自動遞增）。

除了您發現的限制外，該表不支持客戶買一個，半價得到一個的場景。 這將需要兩條具有相同產品和訂單 ID 的記錄。