load navigation properties with filter for Entity Framework 4.3

Question

Few days back I put a question regarding mapping two classes Message and MessageStatusHistory using EF. The mapping is going fine but I am facing some

Answer 1

About your EDIT part: You cannot use ToList() in a projection, just leave it an IEnumerable<T> and convert to a List<T> when you construct the Message. You also don't need to create two list objects, you can switch from the LINQ to Entities query to LINQ to Objects (the second Select) by using AsEnumerable():

var list = (from m in _repository.DBSet
            where m.MessageIdentifier == id
            select new {
                // ...
                Histories = m.Histories.Where(x => x.SenderId == userId)
            })
            .AsEnumerable() // database query is executed here
            .Select(m => new Message {
                // ...
                Histories = m.Histories.ToList(),
                // ...
            }).ToList();

return list;

Be aware that Include has no effect when you use a projection with select. You need to make the properties that you want to include part of the projection - as you already did with select new { Histories.....