在实体框架中将外键值设置回 Null

Question

从记录中删除外键值时，我无法将记录保存到 SQL Server 数据库。

例如，我有一个现有的 BatchDetail 记录，主键 BatchDetailID = 10。它与现有的 RunDetail 记录相关联，主键 RunDetailID = 20，外键 BatchDetailID = 10。我想通过将 RunDetails.BatchDetailID 设置为 null 来解除 RunDetail 与 BatchDetail 的关联。

这是错误信息：

发生参照完整性约束违规：关系一端的“BatchDetail.BatchDetailID”的属性值与另一端的“RunDetail.BatchDetailID”的属性值不匹配。

这是我的类定义：

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，我尝试将其设置回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，都可以正常工作。

谁能看出我的缺点是什么？

Answer 1

问题的根源在于我的问题中没有包含的方法。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();
    }
}

通过创建不Include("RunDetails")的新方法，问题解决了：

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

Answer 2

我插入了 1 个 BatchDetail 和 1 个 RunDetail，如下所示。

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

那么这里就是抛出同样错误的结果。

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);
}

在你的情况下应该是一样的。