[英]Setting a Foreign Key Value Back to Null in Entity Framework
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。
例如,我有一个主键BatchDetailID = 10的现有BatchDetail记录,并且它与一个主键RunDetailID = 20,外键BatchDetailID = 10的现有RunDetail记录关联。我想取消关联RunDetail通过将RunDetails.BatchDetailID设置为null可以从BatchDetail中获取。
这是错误消息:
发生引用完整性约束冲突: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。
这是我的班级定义:
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,而我尝试将其设置回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。
谁能看到我的缺点?
问题的根源是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:
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,可以解决此问题:
public List<BatchDetail> ReadBatchDetailsWithoutRunDetails(int id)
{
using (var myEntities = new MyEntities())
{
return myEntities.BatchDetails.AsNoTracking().ToList();
}
}
我按如下所示插入了1 BatchDetail和1 RunDetail。
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,这里是引发相同错误的结果。
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);
}
您的情况应该相同。
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