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copied!<p>Just stumbled into this oldie...</p> <p>To do this without the dynamic LINQ library, you just need the code as below. This covers most common scenarios including nested properties.</p> <p>To get it working with <code>IEnumerable<T></code> you could add some wrapper methods that go via <code>AsQueryable</code> - but the code below is the core <code>Expression</code> logic needed.</p> <pre><code>public static IOrderedQueryable<T> OrderBy<T>( this IQueryable<T> source, string property) { return ApplyOrder<T>(source, property, "OrderBy"); } public static IOrderedQueryable<T> OrderByDescending<T>( this IQueryable<T> source, string property) { return ApplyOrder<T>(source, property, "OrderByDescending"); } public static IOrderedQueryable<T> ThenBy<T>( this IOrderedQueryable<T> source, string property) { return ApplyOrder<T>(source, property, "ThenBy"); } public static IOrderedQueryable<T> ThenByDescending<T>( this IOrderedQueryable<T> source, string property) { return ApplyOrder<T>(source, property, "ThenByDescending"); } static IOrderedQueryable<T> ApplyOrder<T>( IQueryable<T> source, string property, string methodName) { string[] props = property.Split('.'); Type type = typeof(T); ParameterExpression arg = Expression.Parameter(type, "x"); Expression expr = arg; foreach(string prop in props) { // use reflection (not ComponentModel) to mirror LINQ PropertyInfo pi = type.GetProperty(prop); expr = Expression.Property(expr, pi); type = pi.PropertyType; } Type delegateType = typeof(Func<,>).MakeGenericType(typeof(T), type); LambdaExpression lambda = Expression.Lambda(delegateType, expr, arg); object result = typeof(Queryable).GetMethods().Single( method => method.Name == methodName && method.IsGenericMethodDefinition && method.GetGenericArguments().Length == 2 && method.GetParameters().Length == 2) .MakeGenericMethod(typeof(T), type) .Invoke(null, new object[] {source, lambda}); return (IOrderedQueryable<T>)result; } </code></pre> <hr> <p>Edit: it gets more fun if you want to mix that with <code>dynamic</code> - although note that <code>dynamic</code> only applies to LINQ-to-Objects (expression-trees for ORMs etc can't really represent <code>dynamic</code> queries - <code>MemberExpression</code> doesn't support it). But here's a way to do it with LINQ-to-Objects. Note that the choice of <code>Hashtable</code> is due to favorable locking semantics:</p> <pre><code>using Microsoft.CSharp.RuntimeBinder; using System; using System.Collections; using System.Collections.Generic; using System.Dynamic; using System.Linq; using System.Runtime.CompilerServices; static class Program { private static class AccessorCache { private static readonly Hashtable accessors = new Hashtable(); private static readonly Hashtable callSites = new Hashtable(); private static CallSite<Func<CallSite, object, object>> GetCallSiteLocked( string name) { var callSite = (CallSite<Func<CallSite, object, object>>)callSites[name]; if(callSite == null) { callSites[name] = callSite = CallSite<Func<CallSite, object, object>> .Create(Binder.GetMember( CSharpBinderFlags.None, name, typeof(AccessorCache), new CSharpArgumentInfo[] { CSharpArgumentInfo.Create( CSharpArgumentInfoFlags.None, null) })); } return callSite; } internal static Func<dynamic,object> GetAccessor(string name) { Func<dynamic, object> accessor = (Func<dynamic, object>)accessors[name]; if (accessor == null) { lock (accessors ) { accessor = (Func<dynamic, object>)accessors[name]; if (accessor == null) { if(name.IndexOf('.') >= 0) { string[] props = name.Split('.'); CallSite<Func<CallSite, object, object>>[] arr = Array.ConvertAll(props, GetCallSiteLocked); accessor = target => { object val = (object)target; for (int i = 0; i < arr.Length; i++) { var cs = arr[i]; val = cs.Target(cs, val); } return val; }; } else { var callSite = GetCallSiteLocked(name); accessor = target => { return callSite.Target(callSite, (object)target); }; } accessors[name] = accessor; } } } return accessor; } } public static IOrderedEnumerable<dynamic> OrderBy( this IEnumerable<dynamic> source, string property) { return Enumerable.OrderBy<dynamic, object>( source, AccessorCache.GetAccessor(property), Comparer<object>.Default); } public static IOrderedEnumerable<dynamic> OrderByDescending( this IEnumerable<dynamic> source, string property) { return Enumerable.OrderByDescending<dynamic, object>( source, AccessorCache.GetAccessor(property), Comparer<object>.Default); } public static IOrderedEnumerable<dynamic> ThenBy( this IOrderedEnumerable<dynamic> source, string property) { return Enumerable.ThenBy<dynamic, object>( source, AccessorCache.GetAccessor(property), Comparer<object>.Default); } public static IOrderedEnumerable<dynamic> ThenByDescending( this IOrderedEnumerable<dynamic> source, string property) { return Enumerable.ThenByDescending<dynamic, object>( source, AccessorCache.GetAccessor(property), Comparer<object>.Default); } static void Main() { dynamic a = new ExpandoObject(), b = new ExpandoObject(), c = new ExpandoObject(); a.X = "abc"; b.X = "ghi"; c.X = "def"; dynamic[] data = new[] { new { Y = a }, new { Y = b }, new { Y = c } }; var ordered = data.OrderByDescending("Y.X").ToArray(); foreach (var obj in ordered) { Console.WriteLine(obj.Y.X); } } } </code></pre>

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