在实体框架中设置外键值为空

本文关键字：键值 设置 实体 框架 | 更新日期: 2023-09-27 18:16:52

当从记录中删除外键值时，我无法将记录保存到SQL Server数据库。

作为一个例子，我有一个现有的BatchDetail记录，其主键BatchDetailID = 10。并且它与现有的RunDetail记录相关联，该记录具有主键RunDetailID = 20和外键BatchDetailID = 10。我想通过设置RunDetails来解除RunDetail与BatchDetail的关联。BatchDetailID为空

错误信息如下:

发生了一个引用完整性约束冲突:"BatchDetail"的属性值。关系一端的BatchDetailID与RunDetail的属性值不匹配。"BatchDetailID"

下面是我的类定义:

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值时发生错误，并且我试图将其设置回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值，都可以正常工作。

有人能看出我的缺点是什么吗?

在实体框架中设置外键值为空

问题的根源在于我的问题中没有包括的一个方法。当我检索父BatchDetail记录时，我包含了"RunDetails"记录:

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

通过创建一个不包含Include("RunDetails")的新方法，解决了这个问题:

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

我按如下方式插入1个BatchDetail和1个RunDetail 

using (var db = new AppContext())
{
    db.BatchDetails.Add(new BatchDetail { Id = 1 });
    db.RunDetails.Add(new RunDetail { Id = 1, BatchDetailId = 1 });
    db.SaveChanges();
}

下面是抛出相同错误的结果:

using (var db = new AppContext())
{
    // This is okay.
    var x = new RunDetail { Id = 1, BatchDetailId = 1, BatchDetail = new BatchDetail { Id = 1 } };
    db.RunDetails.Attach(x);
}
using (var db = new AppContext())
{
    // This is okay.
    var x = new RunDetail { Id = 1, BatchDetailId = null, BatchDetail = null };
    db.RunDetails.Attach(x);
}
using (var db = new AppContext())
{
    // This is okay.
    var x = new RunDetail { Id = 1, BatchDetailId = 1, BatchDetail = null };
    db.RunDetails.Attach(x);
}
using (var db = new AppContext())
{
    // A referential integrity constraint violation occurred: The property 
    // value(s) of 'BatchDetail.Id' on one end of a relationship do not match the property 
    // value(s) of 'RunDetail.BatchDetailId' on the other end.
    var x = new RunDetail { Id = 1, BatchDetailId = null, BatchDetail = new BatchDetail { Id = 1 } };
    db.RunDetails.Attach(x);
}
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