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    <p>Based on what everyone has contributed I have come up with the following. </p> <p>It provides bi-directional sorting as well solving the problem inside out. Meaning it didn't make much sense to me that a new Sorter need to be created for every unsorted list of a given type. Why can't this the unsorted list be passed into the sorter. This then means that we could create a signelton instance of the Sorter for our different types...</p> <p>Just an idea:</p> <pre><code>[TestClass] public class SpecifyUserDefinedSorting { private Sorter&lt;Movie&gt; sorter; private IQueryable&lt;Movie&gt; unsorted; [TestInitialize] public void Setup() { unsorted = from m in Movies select m; sorter = new Sorter&lt;Movie&gt;(); sorter.Register("Name", m1 =&gt; m1.Name); sorter.Register("Year", m2 =&gt; m2.Year); } [TestMethod] public void SortByNameThenYear() { var instructions = new List&lt;SortInstrcution&gt;() { new SortInstrcution() {Name = "Name"}, new SortInstrcution() {Name = "Year"} }; var sorted = sorter.SortBy(unsorted, instructions); var movies = sorted.ToArray(); Assert.AreEqual(movies[0].Name, "A"); Assert.AreEqual(movies[0].Year, 2000); Assert.AreEqual(movies[1].Year, 2001); Assert.AreEqual(movies[2].Name, "B"); } [TestMethod] public void SortByNameThenYearDesc() { var instructions = new List&lt;SortInstrcution&gt;() { new SortInstrcution() {Name = "Name", Direction = SortDirection.Descending}, new SortInstrcution() {Name = "Year", Direction = SortDirection.Descending} }; var sorted = sorter.SortBy(unsorted, instructions); var movies = sorted.ToArray(); Assert.AreEqual(movies[0].Name, "B"); Assert.AreEqual(movies[0].Year, 1990); Assert.AreEqual(movies[1].Name, "A"); Assert.AreEqual(movies[1].Year, 2001); Assert.AreEqual(movies[2].Name, "A"); Assert.AreEqual(movies[2].Year, 2000); } [TestMethod] public void SortByNameThenYearDescAlt() { var instructions = new List&lt;SortInstrcution&gt;() { new SortInstrcution() {Name = "Name", Direction = SortDirection.Descending}, new SortInstrcution() {Name = "Year"} }; var sorted = sorter.SortBy(unsorted, instructions); var movies = sorted.ToArray(); Assert.AreEqual(movies[0].Name, "B"); Assert.AreEqual(movies[0].Year, 1990); Assert.AreEqual(movies[1].Name, "A"); Assert.AreEqual(movies[1].Year, 2000); Assert.AreEqual(movies[2].Name, "A"); Assert.AreEqual(movies[2].Year, 2001); } [TestMethod] public void SortByYearThenName() { var instructions = new List&lt;SortInstrcution&gt;() { new SortInstrcution() {Name = "Year"}, new SortInstrcution() {Name = "Name"} }; var sorted = sorter.SortBy(unsorted, instructions); var movies = sorted.ToArray(); Assert.AreEqual(movies[0].Name, "B"); Assert.AreEqual(movies[1].Year, 2000); } [TestMethod] public void SortByYearOnly() { var instructions = new List&lt;SortInstrcution&gt;() { new SortInstrcution() {Name = "Year"} }; var sorted = sorter.SortBy(unsorted, instructions); var movies = sorted.ToArray(); Assert.AreEqual(movies[0].Name, "B"); } private static IQueryable&lt;Movie&gt; Movies { get { return CreateMovies().AsQueryable(); } } private static IEnumerable&lt;Movie&gt; CreateMovies() { yield return new Movie { Name = "B", Year = 1990 }; yield return new Movie { Name = "A", Year = 2001 }; yield return new Movie { Name = "A", Year = 2000 }; } } public static class SorterExtension { public static IOrderedQueryable&lt;T&gt; SortBy&lt;T&gt;(this IQueryable&lt;T&gt; source, Sorter&lt;T&gt; sorter, IEnumerable&lt;SortInstrcution&gt; instrcutions) { return sorter.SortBy(source, instrcutions); } } public class Sorter&lt;TSource&gt; { private readonly FirstPasses _FirstPasses; private readonly FirstPasses _FirstDescendingPasses; private readonly NextPasses _NextPasses; private readonly NextPasses _NextDescendingPasses; public Sorter() { this._FirstPasses = new FirstPasses(); this._FirstDescendingPasses = new FirstPasses(); this._NextPasses = new NextPasses(); this._NextDescendingPasses = new NextPasses(); } public void Register&lt;TKey&gt;(string name, Expression&lt;Func&lt;TSource, TKey&gt;&gt; selector) { this._FirstPasses.Add(name, s =&gt; s.OrderBy(selector)); this._FirstDescendingPasses.Add(name, s =&gt; s.OrderByDescending(selector)); this._NextPasses.Add(name, s =&gt; s.ThenBy(selector)); this._NextDescendingPasses.Add(name, s =&gt; s.ThenByDescending(selector)); } public IOrderedQueryable&lt;TSource&gt; SortBy(IQueryable&lt;TSource&gt; source, IEnumerable&lt;SortInstrcution&gt; instrcutions) { IOrderedQueryable&lt;TSource&gt; result = null; foreach (var instrcution in instrcutions) result = result == null ? this.SortFirst(instrcution, source) : this.SortNext(instrcution, result); return result; } private IOrderedQueryable&lt;TSource&gt; SortFirst(SortInstrcution instrcution, IQueryable&lt;TSource&gt; source) { if (instrcution.Direction == SortDirection.Ascending) return this._FirstPasses[instrcution.Name].Invoke(source); return this._FirstDescendingPasses[instrcution.Name].Invoke(source); } private IOrderedQueryable&lt;TSource&gt; SortNext(SortInstrcution instrcution, IOrderedQueryable&lt;TSource&gt; source) { if (instrcution.Direction == SortDirection.Ascending) return this._NextPasses[instrcution.Name].Invoke(source); return this._NextDescendingPasses[instrcution.Name].Invoke(source); } private class FirstPasses : Dictionary&lt;string, Func&lt;IQueryable&lt;TSource&gt;, IOrderedQueryable&lt;TSource&gt;&gt;&gt; { } private class NextPasses : Dictionary&lt;string, Func&lt;IOrderedQueryable&lt;TSource&gt;, IOrderedQueryable&lt;TSource&gt;&gt;&gt; { } } internal class Movie { public string Name { get; set; } public int Year { get; set; } } public class SortInstrcution { public string Name { get; set; } public SortDirection Direction { get; set; } } public enum SortDirection { //Note I have created this enum because the one that exists in the .net // framework is in the web namespace... Ascending, Descending } </code></pre> <p>Note if you didn't want to have a dependency on SortInstrcution it wouldn't be that hard to change.</p> <p>Hope this helps someone.</p>
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    1. COyou need to change SortInstrcution to SortInstruction
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