c# - 如何在一对多关系 EF 4.3.1 的导航集合中删除后正确清理

Question

在典型的一对多关系中，当我删除 like 时:

var orderEntity = context.Orders.Single(o => o.orderID == entityID);
var baddetail = orderEntity.OrderDetails
                           .Single(od => od.orderDetailID == badOrderDetailID);
orderEntity.OrderDetails.Remove(baddetail);

我得到错误:

The operation failed: The relationship could not be changed because one 
or more of the foreign-key properties is non-nullable. When a change is made 
to a relationship, the related foreign-key property is set to a null value. 
If the foreign-key does not support null values, a new relationship must 
be defined, the foreign-key property must be assigned another non-null value, 
or the unrelated object must be deleted.

作为一个解决方案被提出来扩展 DBContext.SaveChanges()

public override int SaveChanges()
    {

        foreach (OrderDetails od in this.OrderDetails.ToList())
        {
            // Remove OrderDetails without Order.
            if (od.Order == null)
            {
                this.OrderDetail.Remove(od);
            }
        }

        return base.SaveChanges();
    }

但是当 orderID 不可为 null 时，正在检查具有空订单的 OrderDetails 似乎很奇怪。这样做的正确方法是什么？

编辑:例如，当您通过将 Order.OrderDetails 绑定(bind)到 DataGrid 来公开时，就会发生这种奇怪的删除。

Answer 1

你可以这样做:

var orderEntity = context.Orders.Single(o => o.orderID == entityID);var baddetail = orderEntity.OrderDetails.Single(od => od.orderDetailID == badOrderDetailID);context.OrderDetails.Remove(baddetail);

因为在您的示例中您没有删除实体。您正在删除关系。因此它会尝试将 null 设置为您的 FK 列，并且它不可为空，您将获得异常。