getDummySelectSQL example

$this->pingConnection($entityManager);
        }

        return $stack->next()->handle($envelope, $stack);
    }

    private function pingConnection(EntityManagerInterface $entityManager): void
    {
        $connection = $entityManager->getConnection();

        try {
            $connection->executeQuery($connection->getDatabasePlatform()->getDummySelectSQL());
        } catch (DBALException) {
            $connection->close();
            $connection->connect();
        }

        if (!$entityManager->isOpen()) {
            $this->managerRegistry->resetManager($this->entityManagerName);
        }
    }
}