在实体框架中将外键值设置回Null [英] Setting a Foreign Key Value Back to Null in Entity Framework

问题描述

从记录中删除外键值时，我无法将记录保存到SQL Server数据库中。

I have been unable to save a record to a SQL Server database when removing a foreign key value from the record.

例如，我有一个现有的BatchDetail记录具有主键BatchDetailID =10。它与具有主键RunDetailID = 20和外键BatchDetailID = 10的现有RunDetail记录相关联。我想通过将RunDetails.BatchDetailID设置为来将RunDetail与BatchDetail取消关联

As an example, I have an existing BatchDetail record with a primary key BatchDetailID = 10. And it is associated with an existing RunDetail record that has a primary key RunDetailID = 20, and a foreign key BatchDetailID = 10. I want to disassociate the RunDetail from the BatchDetail by setting RunDetails.BatchDetailID to null.

这是错误消息：

参照完整性约束冲突发生：关系的一端 BatchDetail.BatchDetailID的属性值与另一端 RunDetail.BatchDetailID的属性值不匹配。

A referential integrity constraint violation occurred: The property value(s) of 'BatchDetail.BatchDetailID' on one end of a relationship do not match the property value(s) of 'RunDetail.BatchDetailID' on the other end.

这是我的课程定义：

public class RunDetail
{
    public int RunDetailID { get; set; }
    public Nullable<int> BatchDetailID { get; set; }

    public virtual BatchDetail BatchDetail { get; set; }
}

public class BatchDetail
{
    public int BatchDetailID { get; set; }

    public virtual ICollection<RunDetail> RunDetails { get; set; }
}

当 RunDetail 对象具有 BatchDetailID 值，我尝试将其设置回null：

The error occurs when a RunDetail object has a BatchDetailID value, and I try to set it back to null:

public class MyController : Controller
{
    private ISvr _myService;

    public ISvr MyService
    {
        get { return _myService ?? (_myService = new MyHandler().GetMyService()); }

        set
        {
            _myService = value;
        }
    }

    public void UpdateBatch(int id)
    {
        foreach (var batchDetail in MyService.ReadBatchDetails(id))
        {
            var runDetail = MyService.ReadRunDetail(batchDetail.RunDetailID);

            runDetail.BatchDetailID = null;
            runDetail.BatchDetail = null; // I have tried with, and without, this line

            MyService.UpdateRun(runDetail );
        }
    }
}

public class MyHandler
{
    public ISvr GetMyService()
    {
        return new MySvr();
    }
}

[ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Multiple, InstanceContextMode = InstanceContextMode.PerCall)]
public class MySvr : IMySvr
{
    public void UpdateRun(RunDetail runDetail)
    {
        using (var myEntities = new MyEntities())
        {
            myEntities.RunDetails.Attach(runDetail); // This is where the exception hits
            myEntities.Entry(runDetail).State = EntityState.Modified;
            myEntities.SaveChanges();
        }
    }
}

所有其他记录更新，包括将外键值更改为另一个，可以正常工作。

All other record updates, including changing the foreign key value to another, work correctly.

有人可以看到我的缺点吗？

Can anyone see what my flaw is?

推荐答案

问题植根于我未在问题中包含的方法。当我检索父 BatchDetail 记录时，我包括了 RunDetails记录：

The problem was rooted in a method that I did not include in my question. When I retrieved the parent BatchDetail record, I included the "RunDetails" records:

public List<BatchDetail> ReadBatchDetails(int id)
{
    using (var myEntities = new MyEntities())
    {
        return myEntities.BatchDetails
            .Include("RunDetails") // This is the problem
            .AsNoTracking().ToList();
    }
}

通过创建不<$ c的新方法$ c> Include（ RunDetails），问题已解决：

By creating a new method that does not Include("RunDetails"), the problem is resolved:

public List<BatchDetail> ReadBatchDetailsWithoutRunDetails(int id)
{
    using (var myEntities = new MyEntities())
    {
        return myEntities.BatchDetails.AsNoTracking().ToList();
    }
}

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