public function createJoinTable()
    {
        if ($this->joinTableExists() === true) {
            return;
        }

        $q = 'CREATE TABLE \''.$this->joinTable().'\' (
            target_type VARCHAR(255),
            target_id VARCHAR(255),
            target_property VARCHAR(255),
            attachment_type VARCHAR(255),
            attachment_id VARCHAR(255),
            created DATETIME
        )';
        $this->logger->debug($q);
        $this->source()->db()->query($q);
    }