doctrine-manager-reopen.php

<?php

use App\Alien;
use Doctrine\DBAL\DBALException;

$entity = new Alien();

try {
    $this->em->persist($entity);
    $this->em->flush();
} catch (DBALException $e) {
    if (!$this->em->isOpen()) {
        $this->doctrine->resetManager();
        $this->em = $this->doctrine->getManager();
    }
}