linq递归

  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 = , Text = "Item 1", ParentId = },
                new Comment() { Id = , Text = "Item 2", ParentId =  },
                new Comment() { Id = , Text = "Item 3", ParentId =  },
                new Comment() { Id = , Text = "Item 1.1", ParentId =  },
                new Comment() { Id = , Text = "Item 3.1", ParentId =  },
                new Comment() { Id = , Text = "Item 1.1.1", ParentId =  },
                new Comment() { Id = , Text = "Item 2.1", ParentId =  }
            };

            List<Comment> hierarchy = new List<Comment>();
            hierarchy = categories
                            .Where(c => c.ParentId == )
                            .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);
                }
            }
        }