Simple sql join in codeigniter

$data = $this->db
              ->select( 'b.*,a.name as author_name' )
              ->from( 'books b')
              ->join( 'authors a', 'b.author = a.id' , 'left' )             
              ->get()
              ->result_array();
         /* result
        SELECT `b`.*, `a`.`name` as author_name
        FROM (`books` b)
        LEFT JOIN `authors` a ON `b`.`author` = `a`.`id` */