如何从实体框架上下文去附着的实体？ [英] How to de-attach an entity from a Context in Entity Framework?

问题描述

我用EF 4.1库和的DbContext .. POCO用T4模板。
对于每一个库我使用一个单独的DbContext。

我需要更新的对象，具有相关性，在现阶段，我收到此错误

 的实体对象不能由IEntityChangeTracker的多个实例被引用。
 

我想我的问题是怎么一回事，因为是eventObj 和候选人从不同的存储库中创建的。

所以我想解决这个code中的问题，但没有成功。

我的问题？

• 如何摆脱这种错误的？



• 时，可以从上下文中删除候选人？

   公共无效UpdateAddingCandidate（事件是eventObj，候选人人选）{
      事件updatedEvent =新事件（）;
      候选updatedCandidate =新的候选（）;
      updatedEvent =是eventObj;
      updatedCandidate =候选人;
      updatedEvent.Candidate = updatedCandidate;
      db.Entry（updatedEvent）.STATE = EntityState.Modified;
  }
   

修改

 公共无效UpdateAddingCandidate（事件是eventObj，候选人人选）
    {
        / *
        db.Events.AsNoTracking（）;
        db.Candidates.AsNoTracking（）;
        * /
        db.Entry（是eventObj）.STATE = EntityState.Detached;
        db.Entry（候选人）.STATE = EntityState.Detached;        事件updatedEvent =新事件（）;
        候选updatedCandidate =新的候选（）;
        updatedEvent =是eventObj;
        updatedCandidate =候选人;
        updatedEvent.Candidate = updatedCandidate;
        db.Entry（updatedEvent）.STATE = EntityState.Detached;
        db.Entry（updatedEvent）.STATE = EntityState.Modified;    }
 

解决方案

当你试图更新的实体连接到不同的ObjectContext比​​您正在使用更新它的背景下这种错误确实抛出。只有一个ObjectContext的可跟踪实体

您可以分离对象从它的背景下，通过调用：

，其中上下文是实体当前被附加到上下文

 使用（VAR上下文=新UnicornsContext（））
{
    VAR麒麟=新麒麟{名称=永邦，PrincessId = 1};
    context.Entry（麒麟）.STATE = EntityState.Detached;
    context.SaveChanges（）;
}
 

<一个href=\"http://blogs.msdn.com/b/adonet/archive/2011/01/29/using-dbcontext-in-ef-feature-ctp5-part-4-add-attach-and-entity-states.aspx\" rel=\"nofollow\">http://blogs.msdn.com/b/adonet/archive/2011/01/29/using-dbcontext-in-ef-feature-ctp5-part-4-add-attach-and-entity-states.aspx

而在你实现：

 公共无效UpdateAddingCandidate（事件是eventObj，候选人人选）
{
    db.Entry（候选人）.STATE = EntityState.Detached;
    db.SaveChanges（）;    eventObj.Candidate =候选人;
    db.Entry（是eventObj）.STATE = EntityState.Modified;
    db.SaveChanges（）;
}
 

I use EF 4.1 with Repository and DbContext.. POCO with T4 template. For every Repository I use a separate DbContext.

I need to update an object with has a related property, at the moment I receive this error

An entity object cannot be referenced by multiple instances of IEntityChangeTracker.

I suppose my problem is beacuse eventObj and candidate are created from different Repositories.

So i'm trying to solve the problem with this code, with no success.

My question?

• How do I get rid of this error?

• Is is possible remove the candidate from its context?

  public void UpdateAddingCandidate(Event eventObj, Candidate candidate){
      Event updatedEvent = new Event();
      Candidate updatedCandidate = new Candidate();
      updatedEvent = eventObj;
      updatedCandidate = candidate;
      updatedEvent.Candidate = updatedCandidate;
      db.Entry(updatedEvent).State = EntityState.Modified;     
  }
  

EDIT

    public void UpdateAddingCandidate(Event eventObj, Candidate candidate)
    {
        /*
        db.Events.AsNoTracking();
        db.Candidates.AsNoTracking();
        */
        db.Entry(eventObj).State = EntityState.Detached;
        db.Entry(candidate).State = EntityState.Detached;

        Event updatedEvent = new Event();
        Candidate updatedCandidate = new Candidate();
        updatedEvent = eventObj;
        updatedCandidate = candidate;
        updatedEvent.Candidate = updatedCandidate;
        db.Entry(updatedEvent).State = EntityState.Detached;
        db.Entry(updatedEvent).State = EntityState.Modified;

    }

解决方案

This error is indeed thrown when the entity you're trying to update is attached to a different objectcontext than the context you're using to update it. Only one objectcontext can track an entity

You can detach objects from it's context by calling:

where context is the context the entity currently is attached to.

using (var context = new UnicornsContext())
{
    var unicorn = new Unicorn { Name = "Franky", PrincessId = 1};
    context.Entry(unicorn).State = EntityState.Detached;
    context.SaveChanges();
}

http://blogs.msdn.com/b/adonet/archive/2011/01/29/using-dbcontext-in-ef-feature-ctp5-part-4-add-attach-and-entity-states.aspx

And in your implementation:

public void UpdateAddingCandidate(Event eventObj, Candidate candidate)
{
    db.Entry(candidate).State = EntityState.Detached;
    db.SaveChanges();

    eventObj.Candidate = candidate;
    db.Entry(eventObj).State = EntityState.Modified;
    db.SaveChanges();
}

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