LINQ include and Projection - linq

Question

I have some classes defining entities with relationships
Account
has many Conversations [IEnumerable<Conversation> Conversations]
Conversation
has many Participants [IEnumerable<Account> Participants]
has many Messages [IEnumerable<Message> Messages]
Message
has one Sender [Account Sender]
has one Conversation [Conversation Conversation]
I'm trying to write a LINQ query that returns a list of Conversation ordered by date and including related participants and messages.
public async Task<List<Conversation>> FindAllByAccountIdAsync(Int32 id)
{
return await _Db.Conversations
.Where(c => c.Participants.Any(p => p.AccountId == id))
.Include(c => c.Participants)
.Include(c => c.Messages)
.ToListAsync();
}
This do the work but includes to much data i do not really need.
public async Task<List<Conversation>> FindAllByAccountIdAsync(Int32 id)
{
return await _Db.Conversations
.Where(c => c.Participants.Any(a => a.AccountId == id))
.Include(c => c.Participants.Select(a=> new
{
AccountId = a.AccountId,
Profile = new { FullName = a.Profile.FullName,
Email = a.Profile.Email
}
}))
// Only return the last message in
// Eventually I would not return an array with a single object but just the single object inside associated with the property LastMessageIn
.Include(c => c.Messages.OrderBy(m => m.Date).Select(m=> new
{
Body = m.Body,
SenderId = m.Sender.AccountId
}).Last())
.ToListAsync();
}
This script returns a mile long exception
{"message":"An error has occurred.","exceptionMessage":"The Include path expression must refer to a navigation property defined on the type. Use dotted paths for reference navigation properties and the Select operator for collection navigation properties........}
My mind resist understanding and learning LINQ I do not know if its just me but as soon requirements exceeds basic querying and projection it break out of my control
Someone have some hints?

Answer 1

I'm not sure if I understand your question, but I believe you want something like this:
public async Task<List<Conversation>> FindAllByAccountIdAsync(Int32 id)
{
return await _Db.Conversations
.Where(c => c.Participants.Any(p => p.AccountId == id))
.Include(c => c.Participants)
.Include(c => c.Messages)
.Select(c => new
{
Participants = c.Participants.Select(a=> new
{
AccountId = a.AccountId,
Profile = new { FullName = a.Profile.FullName,
Email = a.Profile.Email
}
},
//EDIT: using OrderByDescending and FirstOrDefault
Messages = c.Messages.OrderByDescending(m => m.Date).Select(m=> new
{
Body = m.Body,
SenderId = m.Sender.AccountId
}).FirstOrDefault())
//others properties here
}
.ToListAsync();
}

Answer 2

You cannot project on an Include. An include is simply Eager Loading. The output does not change in the C#. Only the amount of data that is originally loaded (ie performance) changes.
It seems you want a projection and not eager loading, which are completely incompatible concepts.
However I cannot understand what exactly what you are trying to achieve.

Answer 3

public async Task<List<Conversation>> FindAllByAccountIdAsync(Int32 id)
{
return await _Db.Conversations
.Where(c => c.Participants.Any(p => p.AccountId == id))
.Include(c => c.Participants.Select(_=>_))
.Include(c => c.Messages.Select(_=>_))
.ToListAsync();
}
Should be enough.