public class LinqHelper

using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Web;
 using System.Linq.Expressions;
 using System.Reflection;
 
 /// <summary>
 /// Helper methods for link
 /// </summary>
 public class LinqHelper
 {
  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;
  }
 }

Extension methods must be defined in a non-generic static class