linq 재귀속

  public class Comment

    {

        public int Id { get; set; }

        public int ParentId { get; set; }

        public string Text { get; set; }        

        public List<Comment> Children { get; set; }

    }



    class Program

    {

        static void Main()

        {

        List<Comment> categories = new List<Comment>()

            {

                new Comment () { Id = 1, Text = "Item 1", ParentId = 0},

                new Comment() { Id = 2, Text = "Item 2", ParentId = 0 },

                new Comment() { Id = 3, Text = "Item 3", ParentId = 0 },

                new Comment() { Id = 4, Text = "Item 1.1", ParentId = 1 },

                new Comment() { Id = 5, Text = "Item 3.1", ParentId = 3 },

                new Comment() { Id = 6, Text = "Item 1.1.1", ParentId = 4 },

                new Comment() { Id = 7, Text = "Item 2.1", ParentId = 2 }

            };



            List<Comment> hierarchy = new List<Comment>();

            hierarchy = categories

                            .Where(c => c.ParentId == 0)

                            .Select(c => new Comment() { Id = c.Id, Text = c.Text, ParentId = c.ParentId, Children = GetChildren(categories, c.Id) })

                            .ToList();



            HieararchyWalk(hierarchy);



            Console.ReadLine();

        }



        public static List<Comment> GetChildren(List<Comment> comments, int parentId)

        {

            return comments

                    .Where(c => c.ParentId == parentId)

                    .Select(c => new Comment { Id = c.Id, Text = c.Text, ParentId = c.ParentId, Children = GetChildren(comments, c.Id) })

                    .ToList();

        }



        public static void HieararchyWalk(List<Comment> hierarchy)

        {

            if (hierarchy != null)

            {

                foreach (var item in hierarchy)

                {

                    Console.WriteLine(string.Format("{0} {1}", item.Id, item.Text));

                    HieararchyWalk(item.Children);

                }

            }

        }