public function purge()
    {
        if ($this->purger === null) {
            throw new \Exception('Doctrine\Common\DataFixtures\Purger\PurgerInterface instance is required if you want to purge the database before loading your data fixtures.');
        }
        if ($this->logger) {
            $this->log('purging database');
        }
        $this->purger->purge();
    }