/**
* Sets or returns the current sort field.
*
* @param string $b The field to sort by.
*
* @return string If $b is null, returns the previously set value.
*/
public static function sortBy($b = null)
{
if (!is_null($b)) {
self::$_sortBy = $b;
} else {
return self::$_sortBy;
}
}
