code: public static function orderBy($field, $order)
      {
          if (!$order) {
              $order = 'DESC';
          }
          $order = strtoupper($order);
          if (!($order=='ASC' || $order=='DESC')) {
              throw new ClusterpointException("\"->order()\" function: ordering should be DESC or ASC.", 9002);
          }
          if (!(gettype($field)=="string" || $field instanceof Key || $field instanceof Raw)) {
              throw new ClusterpointException("\"->order()\" function: passed field selector is not in valid format.", 9002);
          }
          if ($field instanceof Key) {
              $field =  self::field("{$field}");
          }
          return "{$field} {$order}";
      }
docs: Pass back ORDER BY Clause to append the scope.
  
  @param  mixed  $field
  @param  string $order
  @return string