initializeDatabaseConnectionVariables example

\assert(\is_string($trustedProxies) || \is_array($trustedProxies));
            $trustedHeaderSet = $container->getParameter('kernel.trusted_headers');
            \assert(\is_int($trustedHeaderSet));
            Request::setTrustedProxies(\is_array($trustedProxies) ? $trustedProxies : array_map('trim', explode(',', $trustedProxies)), $trustedHeaderSet);
        }

        foreach ($this->getBundles() as $bundle) {
            $bundle->setContainer($this->container);
            $bundle->boot();
        }

        $this->initializeDatabaseConnectionVariables();

        $this->booted = true;
    }

    public static function getConnection(): Connection
    {
        if (self::$connection) {
            return self::$connection;
        }

        self::$connection = MySQLFactory::create();