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，我有一个主键BatchDetailID = 10的现有BatchDetail记录。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.我想要通过将RunDetails.BatchDetailID设置为null来解除RunDetail与BatchDetail的关联。

以下是错误消息：

发生了参照完整性约束违规：＆＃39; BatchDetail.BatchDetailID＆＃39;的属性值。在一段关系的一端与＆＃39; RunDetail.BatchDetailID＆＃39;的属性值不匹配。在另一端。

以下是我的课程定义：

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值时，会发生错误，我尝试将其设置为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）都能正常工作。

有人能看出我的缺陷是什么吗？

Answer 1

问题根源于我在问题中没有包含的方法。当我检索到父BatchDetail条记录时，我包含了＆＃34; RunDetails＆＃34;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Include("RunDetails")的新方法，问题得以解决：

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();
}

然后这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);
}

在你的情况下应该是一样的。

在实体框架中将外键值设置为空

2 个答案: