EF多对多的疯狂

Question

我有一种方法更新EF中的ReportRecipient对象。基元工作正常;当试图管理与物品对象的M2M关系时，头疼就出现了。

请看看下面的代码：

public IReportRecipient ModifyRecipientWithGroupAssignments(IEnumerable<Guid> groupIds, IReportRecipient recipient) 
    { 
     var entity = Context.ReportRecipients 
      .Include("RecipientGroups") 
      .FirstOrDefault(e => e.ReportRecipientId == recipient.ReportRecipientId) 
      .FromIReportRecipient(recipient); 

     var toRemove = entity.RecipientGroups 
      .Where(e => !groupIds.Contains(e.GroupId)) 
      .ToList(); 

     //remove group assignments that no longer apply 
     foreach (var group in toRemove) 
     { 
      if (group != null) 
      { 
       entity.RecipientGroups.Attach(group); 
       entity.RecipientGroups.Remove(group); 
      } 
     } 

     var toAdd = entity.RecipientGroups 
      .Where(e => groupIds.Contains(e.GroupId)) 
      .ToList(); 

     //add new groups that weren't there before 
     foreach (var group in toAdd) 
     { 
      if (group != null) 
      { 
       entity.RecipientGroups.Attach(group); 
      } 
     } 

     return entity; 
    } 

...我的问题是关于var ToAdd...线。即使我在groupIds中有一组Guid，它们与数据库中的代表RecipientGroup对象的Guids匹配，toAdd总是计算为一个空集合。我认为Contains()函数适用于这种情况;有人能解释我是否做错了什么？

Answer 1

您应该从数据库中加载想要添加的RecipientGroup（我想是Context.RecipientGroups），而不是您想要添加它们的集合（代码示例中的entity.RecipientGroups）。