实体框架。嵌套在.Include中 [英] Entity Framework .Where nested in .Include

问题描述

我正在尝试使用EF5代码执行数据库查找。基本结构和表关系如下：

I'm attempting to perform a db lookup using EF5 code-first. The basic structure and table relationships are as follows;

public partial class Member
{
    public int    RecordID {get; set;}
    public string Name     {get; set;}
    ...etc.
    public virtual ICollection<MemberLink> MasterLinks {get; set;}
    public virtual ICollection<MemberLink> SlaveLinks {get; set;}
    public virtual ICollection<Message>    ReceivedMessages {get; set;}
    public virtual ICollection<Message>    SentMessages {get; set;}
}

public partial class MemberLink
{
    public int            RecordID     {get; set;}
    public virtual Member MasterMember {get; set;}
    public virtual Member SlaveMember  {get; set;}
    ...etc.
}

public partial class Message
{
    public int            RecordID  {get; set;}
    public virtual Member Sender    {get; set;}
    public virtual Member Recipient {get; set;}
    ...etc.
}

现在，我试图执行的查询是使用 MemberLinkRepository ，看起来像;

Now, the query I'm trying to perform is using the MemberLinkRepository, and looks like;

public IList<MemberLink> GetMasterLinks(int p_MemberID)
{
    return Get()
           .Include ( memberLink => memberLink.MasterMember )
           .Include ( memberLink => memberLink.SlaveMember )
           .Include ( memberLink => memberLink.MasterMember.ReceivedMessages
                      .Where(
                      msg => msg.Sender.RecordID == memberLink.SlaveMember.RecordID) )
           .Where ( memberLink => memberLink.MasterMember.RecordID == p_MemberID)
           .ToList();

除了EF似乎不喜欢嵌套的Where。我可以将它分成两个独立的存储库调用（实际上，它看起来像我可能必须这样做），但是为了减少对db的调用，我试图在一次犯规中执行此操作。有没有人知道如何在一个单一的查询中实现这一点？

Except EF doesn't seem to like the nested Where. I could split this out into 2 separate repository calls (and indeed, it's looking like I might have to do that) but in the interest of reducing calls to the db I'm trying to do it in one foul swoop. Does anyone know how I can achieve this in one single query?

我希望代码说明我正在做什么...如果没有，我会尝试并解释一点更好。

I hope the code illustrates what I'm trying to do... If not, I'll try and explain a little better.

推荐答案

简短的答案是否定的，EF不会让你使用包含（）。

The short answer is no, EF will not let you do that using Include().

如果允许，请考虑结果：在某种情况下，您的 MemberLink。 MasterMember.ReceivedMessages 将被完全填充，在另一个相同的查找对象 MemberLink.MasterMember.ReceivedMessages 实际上是一个子集的消息！如果您尝试添加到ReceivedMessages，会发生什么？如果添加与过滤器不匹配怎么办？这是一个伤害的袋子。

Think about the result if it let you do this: in one case your MemberLink.MasterMember.ReceivedMessages will be fully populated, on another identical looking object MemberLink.MasterMember.ReceivedMessages is actually a sub-set of messages! What happens if you try to add to the ReceivedMessages? What if the addition doesn't match the filter? It is a bag of hurt.

答案是使用预测：

public IList<MemberLinkWithFiltereredMessages> GetMasterLinks(int p_MemberID)
{
    return Get()
        .Include(memberLink => memberLink.MasterMember)
        .Include(memberLink => memberLink.SlaveMember)
        .Where(memberLink => memberLink.MasterMember.RecordID == p_MemberID)
        .Select(memberLink => new MemberLinkWithFilteredMessages
        {
            MemberLink = memberLink,
            FilteredMessages = memberLink.MasterMember.ReceivedMessages
                .Where(msg => msg.Sender.RecordID == memberLink.SlaveMember.RecordID)
        })
        .ToList();
}

你真正在做的是要求一个特定的信息子集，所以要明确。

What you are really doing is asking for a specific sub-set of information, so be explicit about it.

这篇关于实体框架。嵌套在.Include中的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！