Entity Framework .Where nested in .Include - entity-framework

Question

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

Answer 1

The short answer is no, EF will not let you do that using Include().
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.
The answer is to use projections:
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();
}
What you are really doing is asking for a specific sub-set of information, so be explicit about it.