我从DbContext得到以下错误：“违反了多重约束.关系”MyModel.FK_ChildEntities_MyEntities“的角色”MyEntity“具有多重性1或0..1.

使用ASP.NET,实体框架4

使用独立实体

该错误发生在我第二次尝试重新连接一个实体到dbcontext.该方案是一个不成功的保存,然后是重新尝试.

我在会话中有一个分离的实体.用户更改表单中的属性,添加内容,删除内容,最终点击保存.我从dbcontext的一个新实例中获取实体的附件副本,将更改从分离的实体应用到附加实体,验证,查找错误并中止.用户更改任何内容并再次保存.

第二个保存,整个保存过程重复,只有这一次,所有这一切都到了.几乎所有的东西都被重复,造成一个错误或者其他的或全部的错误.来自视图和查找表的仅作为引用的值将创建新的和重新分配的id.大多数这些问题我已经能够解决,但我遗留了多重错误.正在创建子元素作为其他子元素的精确副本,直到唯一的ID,仅在添加状态.或者,如果我引用某些属性,而不是克隆未修改的小孩,它会删除新的.无论哪种方式,代码都没有像第一次那样执行.

我抛弃了dbcontext和附件实体的实例,每次保存尝试.我认为这足以恢复任何变化,但必须坚持的事情.唯一没有被忽略或重置的是分离的实体,这是在会话中,但我没有对其进行任何更改.至少不是直接

代码(非常简化)是这样的：

void Save()
{
using (var context = new MyContext())
{
   // detached entity from session
   MyEntity detachedEntity = (MyEntity)Session["DetachedEntity"];

   // attached entity from context
   MyEntity attachedEntity = context.MyEntities.Single(x=>x.id == detachedEntity.id);       


   // <remove children representing lookup table elements from detachedEntity to prevent duplicates>
   // <remove children representing view elements from detachedEntity to prevent duplicates>


   // <apply changes from detachedEntity to attachedEntity>


   // <add new children>
   // <remove deleted children>
   // <update modified children>


   // <set entity state to unchanged on view and lookup elements of attachedEntity to ensure no duplicates...>


   // <validate>


   if (errors.count>0)
     // <report errors>
   else
     context.SaveChanges();
}
}

作为示例,这会产生多重错误：

// represents first save:
    using (var context = new MyContext())
    {
       // detached entity from session
       MyEntity detachedEntity = (MyEntity)Session["DetachedEntity"];

       // attached entity from context
       MyEntity attachedEntity = context.MyEntities.Single(x=>x.id == detachedEntity.id);       

       int debug1 = context.ChangeTracker.Entries<ChildEntity>().Count(); // debug1 == 0;

       attachedEntity.ChildEntities.Add(detachedEntity.ChildEntities.First());

       int debug2 = context.ChangeTracker.Entries<ChildEntity>().Count(); // debug2 == 1;

    }

// represents second save:
    using (var context = new MyContext())
    {
       // detached entity from session
       MyEntity detachedEntity = (MyEntity)Session["DetachedEntity"];

       // attached entity from context
       MyEntity attachedEntity = context.MyEntities.Single(x=>x.id == detachedEntity.id);    

       int debug1 = context.ChangeTracker.Entries<ChildEntity>().Count(); // debug1 == 0;

       attachedEntity.ChildEntities.Add(detachedEntity.ChildEntities.First());

       int debug2 = context.ChangeTracker.Entries<ChildEntity>().Count(); // multiplicity error;

    }

ChildEntity detachedChild = detachedEntity.ChildEntities.First();
attachedEntity.ChildEntities.Add(new ChildEntity { 
   propertyA = detachedChild.propertyA,propertyB = detachedChild.propertyB
});

attachedEntity.ChildEntities.Add(detachedEntity.ChildEntities.First());