违反了多重约束.关系'...'的作用'...'具有多重性1或0..1

Question

我从我的DbContext收到以下错误:"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,Entity Framework 4

使用分离的实体

第二次尝试将实体重新附加到dbcontext时发生错误.该方案是一次失败的保存,然后是重新尝试.

我在会话中有一个独立的实体.用户更改表单中的属性,添加内容,删除内容,最后单击保存.我从dbcontext的新实例获取实体的附加副本,将更改从分离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.

在第二次保存时,整个保存过程重复进行,只有这一次一切都变成了地狱.几乎所有东西都是重复的,导致一个错误或另一个或全部错误.视图和查找表中仅应该是引用的值将被创建为新的并重新分配的id.我已经能够解决的大多数问题,但我留下了多重性错误.子元素被创建为其他子元素的精确副本,直到唯一ID,仅在已添加状态.或者,如果我引用某些属性,而不是克隆未修改的子项,则会删除新的属性.无论哪种方式,没有任何代码像第一次执行那样执行.

我正在丢弃每个保存尝试的dbcontext和附加实体的实例.我认为这足以恢复任何变化,但必须坚持下去.唯一没有丢弃或重置的是分离的实体,它在会话中,但我不做任何更改.至少不是直接的.

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();
}
}

例如,这会产生多重性错误:

// 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;

    }

Answer 1

不知何故,dbcontext会记住添加了哪些对象.如果完全相同的对象出现两次,它......吹

而不是将我的分离实体中的子实体添加到附加的实体,我应该创建每个孩子的新副本

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

代替

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

Answer 2

问题是应该为detaachedChild.parent分配attachmentParent.

foreach(var detachedEntity in detachedEntities)
{
     attachedEntity.ChildEntities.Add(detachedEntity); 
     detachedEntity.ParentEntity = attachedEntity;
}