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LINQ to Tree - A Generic Technique for Querying Tree-like Structures

, 4 Mar 2010 CPOL
This article presents a generic approach to applying LINQ queries to tree like structures. Using T4 templates for code generation, LINQ to VisualTree (WPF), LINQ to WinForms, and LINQ to FileSystem APIs are constructed.





using System.Linq;
using System.Collections.Generic;
using System;
 



using System.IO;

namespace LinqToFileSystem
{
	/// <summary>
    /// Defines an interface that must be implemented to generate the LinqToTree methods
    /// </summary>
    /// <typeparam name="T"></typeparam>
    public interface ILinqTree<T>
    {
        IEnumerable<T> Children();

        T Parent { get; }
    }
  
    public static class TreeExtensions
    {
        /// <summary>
        /// Returns a collection of descendant elements.
        /// </summary>
	    public static IEnumerable<DirectoryInfo> Descendants(this DirectoryInfo item)
        {
            ILinqTree<DirectoryInfo> adapter = new FileSystemTreeAdapter(item);
            foreach (var child in adapter.Children())
            {
                yield return child;

                foreach (var grandChild in child.Descendants())
                {
                    yield return grandChild;
                }
            }
        }    
           
        /// <summary>
        /// Returns a collection containing this element and all descendant elements.
        /// </summary>
	    public static IEnumerable<DirectoryInfo> DescendantsAndSelf(this DirectoryInfo item)
        {            
            yield return item;

            foreach (var child in item.Descendants())
            {
                yield return child;
            }
        }
        
        /// <summary>
        /// Returns a collection of ancestor elements.
        /// </summary>
	    public static IEnumerable<DirectoryInfo> Ancestors(this DirectoryInfo item)
        {
            ILinqTree<DirectoryInfo> adapter = new FileSystemTreeAdapter(item);
            
            var parent = adapter.Parent;
            while(parent != null)
            {
                yield return parent;
                adapter = new FileSystemTreeAdapter(parent);
                parent = adapter.Parent;
            }
        } 
        
        /// <summary>
        /// Returns a collection containing this element and all ancestor elements.
        /// </summary>
	    public static IEnumerable<DirectoryInfo> AncestorsAndSelf(this DirectoryInfo item)
        {
            yield return item;

            foreach (var ancestor in item.Ancestors())
            {
                yield return ancestor;
            }
        }
        
        /// <summary>
        /// Returns a collection of child elements.
        /// </summary>
	    public static IEnumerable<DirectoryInfo> Elements(this DirectoryInfo item)
        {
            ILinqTree<DirectoryInfo> adapter = new FileSystemTreeAdapter(item);
            foreach (var child in adapter.Children())
            {
                yield return child;                
            }
        }
        
        /// <summary>
        /// Returns a collection of the sibling elements before this node, in document order.
        /// </summary>
	    public static IEnumerable<DirectoryInfo> ElementsBeforeSelf(this DirectoryInfo item)
        {
			if (item.Ancestors().FirstOrDefault()==null)
				yield break;
            foreach (var child in item.Ancestors().First().Elements())
            {
				if (child.FullName == item.FullName)
					break;
                yield return child;                
            }
        }
        
        /// <summary>
        /// Returns a collection of the elements after this node, in document order.
        /// </summary>
	    public static IEnumerable<DirectoryInfo> ElementsAfterSelf(this DirectoryInfo item)
        {
			if (item.Ancestors().FirstOrDefault()==null)
				yield break;
            bool afterSelf = false;
            foreach (var child in item.Ancestors().First().Elements())
            {
				if (afterSelf)
					yield return child;                
                
                if (child.FullName == item.FullName)
					afterSelf=true;
            }
        }
        
        /// <summary>
        /// Returns a collection containing this element and all child elements.
        /// </summary>
	    public static IEnumerable<DirectoryInfo> ElementsAndSelf(this DirectoryInfo item)
        {
            yield return item;

            foreach (var child in item.Elements())
            {
                yield return child;
            }
        }
    }
    
    public static class EnumerableTreeExtensions
    {
		/// <summary>
        /// Applies the given function to each of the items in the supplied
        /// IEnumerable.
        /// </summary>
        private static IEnumerable<DirectoryInfo> DrillDown(this IEnumerable<DirectoryInfo> items,
            Func<DirectoryInfo, IEnumerable<DirectoryInfo>> function)
        {
            foreach(var item in items)
            {
                foreach(var itemChild in function(item))
                {
                    yield return itemChild;
                }
            }
        }

    
        /// <summary>
        /// Returns a collection of descendant elements.
        /// </summary>
	    public static IEnumerable<DirectoryInfo> Descendants(this IEnumerable<DirectoryInfo> items)
        {
            return items.DrillDown(i => i.Descendants());
        }    
           
        /// <summary>
        /// Returns a collection containing this element and all descendant elements.
        /// </summary>
	    public static IEnumerable<DirectoryInfo> DescendantsAndSelf(this IEnumerable<DirectoryInfo> items)
        {            
            return items.DrillDown(i => i.DescendantsAndSelf());
        }
        
        /// <summary>
        /// Returns a collection of ancestor elements.
        /// </summary>
	    public static IEnumerable<DirectoryInfo> Ancestors(this IEnumerable<DirectoryInfo> items)
        {
            return items.DrillDown(i => i.Ancestors());
        } 
        
        /// <summary>
        /// Returns a collection containing this element and all ancestor elements.
        /// </summary>
	    public static IEnumerable<DirectoryInfo> AncestorsAndSelf(this IEnumerable<DirectoryInfo> items)
        {
            return items.DrillDown(i => i.AncestorsAndSelf());
        }
        
        /// <summary>
        /// Returns a collection of child elements.
        /// </summary>
	    public static IEnumerable<DirectoryInfo> Elements(this IEnumerable<DirectoryInfo> items)
        {
            return items.DrillDown(i => i.Elements());
        }
        
        /// <summary>
        /// Returns a collection containing this element and all child elements.
        /// </summary>
	    public static IEnumerable<DirectoryInfo> ElementsAndSelf(this IEnumerable<DirectoryInfo> items)
        {
            return items.DrillDown(i => i.ElementsAndSelf());
        }

    }
}

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This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Colin Eberhardt
Architect Scott Logic
United Kingdom United Kingdom
I am CTO at ShinobiControls, a team of iOS developers who are carefully crafting iOS charts, grids and controls for making your applications awesome.
 
I am a Technical Architect for Visiblox which have developed the world's fastest WPF / Silverlight and WP7 charts.
 
I am also a Technical Evangelist at Scott Logic, a provider of bespoke financial software and consultancy for the retail and investment banking, stockbroking, asset management and hedge fund communities.
 
Visit my blog - Colin Eberhardt's Adventures in .NET.
 
Follow me on Twitter - @ColinEberhardt
 
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