public function get_columns() {
        if (isset($this->_columns)) {
            return $this->_columns;
        }

        global $USER, $CFG;

        $filename = $CFG->tempdir.'/csvimport/'.$this->_type.'/'.$USER->id.'/'.$this->_iid;
        if (!file_exists($filename)) {
            return false;
        }
        $fp = fopen($filename, "r");
        $line = fgetcsv($fp);
        fclose($fp);
        if ($line === false) {
            return false;
        }
        $this->_columns = $line;
        return $this->_columns;
    }