protected function init() {
        if (isset($this->extdb)) {
            return !empty($this->extdb);
        }

        $dbdriver = $this->get_config('dbdriver');
        if (empty($dbdriver)) {
            $this->extdb = false;
            return false;
        }
        list($dblibrary, $dbtype) = explode('/', $dbdriver);

        if (!$db = \moodle_database::get_driver_instance($dbtype, $dblibrary, true)) {
            debugging("Unknown driver $dblibrary/$dbtype", DEBUG_DEVELOPER);
            $this->extdb = false;
            return false;
        }

        $dboptions = array();
        $dboptions['dbpersist'] = $this->get_config('dbpersist', '0');
        $dboptions['dbsocket'] = $this->get_config('dbsocket', '');
        $dboptions['dbport'] = $this->get_config('dbport', '');
        $dboptions['dbschema'] = $this->get_config('dbschema', '');
        $dboptions['dbcollation'] = $this->get_config('dbcollation', '');
        $dboptions['dbhandlesoptions'] = $this->get_config('dbhandlesoptions', false);
        try {
            $db->connect($this->get_config('dbhost'), $this->get_config('dbuser'), $this->get_config('dbpass'),
                $this->get_config('dbname'), false, $dboptions);
            $tables = $db->get_tables();
            if (!in_array($this->get_config('dbtable'), $tables)) {
                debugging('Cannot find the specified table', DEBUG_DEVELOPER);
                $this->extdb = false;
                return false;
            }
        } catch (\moodle_exception $e) {
            debugging('Cannot connect to external database: ' . $e->getMessage(), DEBUG_DEVELOPER);
            $this->extdb = false;
            return false;
        }

        $this->extdb = $db;
        return true;
    }