4C/GummingCommon/Services/OrderExtension.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Linq.Expressions;
using System.Reflection;

namespace GummingCommon
{
    public static class OrderExtension
    {
        public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> source, string property)
        {
            return ApplyOrder<T>(source, property, "OrderBy");
        }
        public static IQueryable<T> OrderBy<T>(this IQueryable<T> source, string property, string ascending)
        {
            var param = Expression.Parameter(typeof(T), "p");
            var prop = Expression.Property(param, property);
            var exp = Expression.Lambda(prop, param);
            string method = (ascending.ToLower() == "asc" || ascending == "true") ? "OrderBy" : "OrderByDescending";
            Type[] types = new Type[] { source.ElementType, exp.Body.Type };
            var mce = Expression.Call(typeof(Queryable), method, types, source.Expression, exp);
            return source.Provider.CreateQuery<T>(mce);
        }       

        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;
        }
    }
}