public function __construct($to_table, $join_table, $from_column = null, $from_join_column = null, $to_join_column = null, $to_column = null) { parent::__construct($to_table, $from_column, $to_column); $this->_join_table = $join_table; $this->_from_join_column = $from_join_column; $this->_to_join_column = $to_join_column; }