/**
* Set the sorting method.
*
* @param string[optional] $sortingMethod Set the sorting method that should be used, possible values are: desc, asc.
*/
public function setSortingMethod($sortingMethod = 'desc')
{
$aAllowedSortingMethods = array('asc', 'desc');
// set sorting method
self::$sortingMethod = SpoonFilter::getValue($sortingMethod, $aAllowedSortingMethods, 'desc');
}
