code: public function orderBy($orderBy)
      {
          if (is_array($orderBy) === true) {
              $this->orderBy = '';
              foreach ($orderBy as $key => $elem) {
                  $this->orderBy .= $key . ' ' . $elem . ', ';
              }
              $this->orderBy = substr($this->orderBy, 0, -2);
          } else {
              $this->orderBy = $orderBy;
          }
  
          return $this;
      }
docs: Set order by clause.
  
  @param  array|string $orderBy order by clause
  @return Update       this