Set key inside order by clause in linq dynamically

I need to set the key in the OrderBy clause using linq , where the key is a property of an object. I only have the property name with me. How can i set the property dynamically.

class Obj 
{
    string Level
    {
       get;
       set;
    }
}

List<Obj> objList;

objList.OrderByDescending(x => x.Level); => "here i only have property name."

Hope any one can help

Thanks Sunil

You can do this by Extension Methods and Creating Expression Trees dynamically like

public static IOrderedQueryable<T> OrderByDescending<T>(this IQueryable<T> enumerable, string sortColumn)
{
    var param = Expression.Parameter(typeof(T), "x");
    var mySortExpression = Expression.Lambda<Func<T, object>>(Expression.Property(param, sortColumn), param);
    return enumerable.OrderByDescending(mySortExpression);;
 }

and for OrderBy

public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> enumerable, string sortColumn)
{
    var param = Expression.Parameter(typeof(T), "x");
    var mySortExpression = Expression.Lambda<Func<T, object>>(Expression.Property(param, sortColumn), param);
    return enumerable.OrderBy(mySortExpression);;
 }

and you can combine these two in one like

public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> enumerable, string sortColumn, string direction)
{
     var param = Expression.Parameter(typeof(T), "x");
     var mySortExpression = Expression.Lambda<Func<T, object>>(Expression.Property(param, sortColumn), param);

      IOrderedQueryable<T> iQuery;
      switch(direction)
      {
          case "desc": 
            iQuery = enumerable.OrderByDescending(mySortExpression);
            break;
          case "asc":
          default :
            iQuery = enumerable.OrderBy(mySortExpression);
            break;
      }
      return iQuery;
 }

Then you can call it like objList.OrderBy("Level","asc") //For Ascending objList.OrderBy("Level","desc") //For Descending

Hope It will help