Recursive LINQ query: select item and all children with subchildren

Question

Is there any way to write a LINQ (or procedural style) query, that can select an item and all children with one query? I have entity:

public class Comment
{
         


        

Answer 1

   public class Comment
    {
        public int Id { get; set; }
        public int ParentId { get; set; }
        public string Text { get; set; }        
        public List Children { get; set; }
    }

    class Program
    {
        static void Main()
        {
        List categories = new List()
            {
                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 hierarchy = new List();
            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 GetChildren(List 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 hierarchy)
        {
            if (hierarchy != null)
            {
                foreach (var item in hierarchy)
                {
                    Console.WriteLine(string.Format("{0} {1}", item.Id, item.Text));
                    HieararchyWalk(item.Children);
                }
            }
        }