public function get_dbh()
    {
        if (!$this->db) {
            $this->db = rcube_db::factory(
                $this->config->get('db_dsnw'),
                $this->config->get('db_dsnr'),
                $this->config->get('db_persistent')
            );

            $this->db->set_debug((bool)$this->config->get('sql_debug'));
        }

        return $this->db;
    }