symfony - 无法将 EntityManager 注入(inject) Twig 扩展

Question

我在将 EntityManger 注入(inject) Symfony2 twig-extension 时遇到问题。我做了以下事情:

我注册了一个新的 Twig 扩展并创建了一个类。所有这一切都在发挥作用。现在我想访问数据库并尝试注入(inject)EntityManager 学说。我的第一步是将 EM 作为参数添加到构造函数中:

use XYZ\BlubBundle\Utils\SessionHelper;

class SessionHelperExtension extends \Twig_Extension
{
    private $em;
    private $conn;
    protected $sessionHelper;

    public function __construct(\Doctrine\ORM\EntityManager $em, \XYZ\BlubBundle\Utils\SessionHelper $sessionHelper) {
        $this->em = $em;
        $this->conn = $em->getConnection();
        $this->sessionHelper = $sessionHelper;
    }

    [...]
}

?>

然后我将以下行添加到 service.yaml 中:

twig.extension.sessionHelper:
    class: XYZ\BlubBundle\Extensions\SessionHelperExtension
    arguments: [@session_helper, @doctrine.orm.entity_manager]
    tags:
        - { name: twig.extension }

我自己的服务“sessionHelper”被注入(inject)没有问题，但EntityManager始终为“null”。我在这里做错了什么？

编辑:我收到以下异常:

Catchable Fatal Error: Argument 2 passed to
XYZ\BlubBundle\Extensions\SessionHelperExtension::__construct() must be an instance of
Doctrine\ORM\EntityManager, none given, 
called in /.../Symfony/app/cache/dev/appDevDebugProjectContainer.php on line 2918 and 
defined in /.../Symfony/src/XYZ/BlubBundle/Extensions/SessionHelperExtension.php line 12

Answer 1

public function __construct(
    \Doctrine\ORM\EntityManager $em, 
    \XYZ\BlubBundle\Utils\SessionHelper $sessionHelper
) {

是错误的 - 您需要保持与 yml 中相同的顺序:

public function __construct(
    \XYZ\BlubBundle\Utils\SessionHelper $sessionHelper, 
    \Doctrine\ORM\EntityManager $em
) {

更新

试试这个:http://www.coderelic.com/2012/06/querying-the-database-from-a-twig-extension-in-symfony-2/