实体框架 .Where 嵌套在 .Include

Question

我正在尝试使用 EF5 代码优先执行数据库查找。基本结构和表关系如下；

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，我尝试执行的查询正在使用 MemberLinkRepository，看起来像；

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。我可以将其拆分为 2 个单独的存储库调用（实际上，看起来我可能必须这样做），但为了减少对数据库的调用，我试图一口气完成它。有谁知道我如何在一个查询中实现这一目标？

我希望代码说明了我正在尝试做的事情......如果没有，我会尝试解释得更好。

Answer 1

简短的回答是否定的，EF 不会让你使用 Include() 这样做。

考虑一下结果是否允许您这样做：在一种情况下，您的MemberLink.MasterMember.ReceivedMessages 将被完全填充，而在另​​一个外观相同的对象上MemberLink.MasterMember.ReceivedMessages 实际上是消息的子集！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？这是一袋伤害。

答案是使用投影：

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();
}

您实际上是在询问特定的信息子集，因此请明确说明。