c# – 使用EF更新PK时出错

[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,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,ErrorMessageResourceName = "Model_Range_Float_Error")]
    public float Discount { get; set; }
}

问题是,当我尝试使用新产品更新OrderDetail项时,我得到异常：

属性“ProductID”是对象的关键信息的一部分,无法修改.

代码是：

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();

我做了一些谷歌并找到了[this solution],说这样做的方法是创建新产品的新实例并关联到Order_Detail的产品导航属性.

但这样做我得到另一个例外：

发生了引用完整性约束冲突：当依赖对象为Unchanged时,除非将其设置为关联的主体对象,否则无法更改作为参照完整性约束一部分的主键属性.必须跟踪主要对象,并且不标记为删除.

修改后的代码：

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);

        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();

我该怎么做才能让用户更改详细信息项中的产品？我真的不喜欢删除整个记录并使用新产品重新创建它的想法.闻起来很糟糕！

谢谢！