Rendering a hierarchy using LINQ?

Question

Let say we have a class

Category
{
   ID,
   Name,
   ParentID
}

and a List

1, \'Item 1\', 0
2, \'Item 2\', 0
3, \'Item 3\'         


        

Answer 1

You can use recursion:

public class Category
{
    public int ID { get; set; }
    public string Name { get; set; }
    public int ParentID { get; set; }
    public List Children { get; set; }
}

class Program
{
    static void Main()
    {
        List categories = new List()
        {
            new Category () { ID = 1, Name = "Item 1", ParentID = 0},
            new Category() { ID = 2, Name = "Item 2", ParentID = 0 },
            new Category() { ID = 3, Name = "Item 3", ParentID = 0 },
            new Category() { ID = 4, Name = "Item 1.1", ParentID = 1 },
            new Category() { ID = 5, Name = "Item 3.1", ParentID = 3 },
            new Category() { ID = 6, Name = "Item 1.1.1", ParentID = 4 },
            new Category() { ID = 7, Name = "Item 2.1", ParentID = 2 }
        };

        List hierarchy = new List();                        
        hierarchy = categories
                        .Where(c => c.ParentID == 0)
                        .Select(c => new Category() { ID = c.ID, Name = c.Name, ParentID = c.ParentID, Children = GetChildren(categories, c.ID) })
                        .ToList();

        HieararchyWalk(hierarchy);            

        Console.ReadLine();
    }        

    public static List GetChildren(List categories, int parentId)
    {            
        return categories
                .Where(c => c.ParentID == parentId)
                .Select(c => new Category { ID = c.ID, Name = c.Name, ParentID = c.ParentID, Children = GetChildren(categories, 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.Name));
                HieararchyWalk(item.Children);                    
            }
        }
    }        
}