using System;

using System.Data.Entity;

public class Program

{

    public static void Main()

    {

        var db = new DbContext();

        db.Primarys

            .Include(p => p.Secondary)

            .Where(p => p.Secondary.OwnerId = 1)

            .GroupBy(p => p.TypeId)

            .Select(g => g.OrderByDescending(p => p.CreatedOn)

                    .FirstOrDefault())

            .ToList();

    }

    public class Primary

    {

        public int PrimaryId { get; set; }

        public int TypeId { get; set; }

        public DateTime CreatedOn { get; set; }

        public Secondary Secondary { get; set; }

    }

    public class Secondary

    {

        public int PrimaryId { get; set; }

        public int OwnerId { get; set; }

    }

​

    public class DbContext

    {

        public DbSet<Primary> Primarys { get; set; }

        public DbSet<Secondary> Secondarys { get; set; }

    }

}