using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        const int page = 1;

        const int pageSize = 15;

        var forums = new List<Forum>

        {

            new Forum

            {

                Id = 1,

                Name = "Forum 1",

                Created = DateTime.Now,

                SubForums = new List<Forum>

                {

                    new Forum {Id = 2, ParentId = 1, Name = "Forum 2"},

                        new Forum {Id = 3, ParentId = 1, Name = "Forum 3"}

                }

            }

        };

        var data = forums

            .Where(f => !f.ParentId.HasValue)

            .OrderByDescending(f => f.Name)

            .Skip((page - 1)*pageSize)

            .Take(pageSize)

            .Select(f => new ForumDTO

                    {

                        Id = f.Id,

                        Name = f.Name,

                        SubForums = f.SubForums.Select(sf => new ForumDTO

                                                       {

                                                           Id = sf.Id,

                                                           Name = sf.Name,

                                                           SubForums = null

                                                       }).ToList()

                    }).ToList();

        foreach (var d in data)

        {

            Console.WriteLine(d.Name);

            if (d.SubForums.Count <= 0) continue;

            foreach (var subForum in d.SubForums)

            {

                Console.WriteLine("\t"+ subForum.Name);

            }

        }       

    }

}

​

public class Forum

{

    public Forum()

    {

        SubForums = new List<Forum>();

    }

    public int Id { get; set; }

    public int? ParentId { get; set; }

    public string Name { get; set; }

    public DateTime Created { get; set; }

    public virtual Forum Parent { get; set; }

    public virtual ICollection<Forum> SubForums { get; set; }

}

​

public class ForumDTO

{

    public int Id { get; set; }

    public int? ParentId { get; set; }

    public string Name { get; set; }

    public DateTime? Created { get; set; }

    public ForumDTO Parent { get; set; }

    public List<ForumDTO> SubForums { get; set; }

}