define doctrine as service in symfony2 DI-container

doctrine.yml

parameters:

    doctrine_cache.class: Doctrine\Common\Cache\ArrayCache
    doctrine_metadata.class: Doctrine\Common\Annotations\Reader
    doctrine_configuration.class: Doctrine\ORM\Configuration
    doctrine_entity_manager.class: Doctrine\ORM\EntityManagerInterface
    doctrine_entity_manager_factory.class: Doctrine\ORM\EntityManager

    doctrine.proxy_dir.path: '/path/to/proxy'
    doctrine.proxy.namespace: 'Project\Proxies'
    doctrine.entities.path: '/path/to/lib/MyProject/Entities'

    doctrine.connection.config: { driver: %db.driver%, user: %db.user%, password: %db.password%, dbname: %db.name% }

services:

    doctrine_cache:
        class: %doctrine_cache.class%
        public: false

    doctrine_metadata_driver:
        public: false
        class: %doctrine_metadata.class%
        factory: [@doctrine_configuration, 'newDefaultAnnotationDriver' ]
        arguments:
          - [ %doctrine.entities.path% ]

    doctrine_configuration:
        class: %doctrine_configuration.class%
        public: false
        calls:
          - [ setMetadataCacheImpl, [@doctrine_cache] ]
          - [ setMetadataDriverImpl, [@doctrine_metadata_driver] ]
          - [ setQueryCacheImpl, [@doctrine_cache] ]
          - [ setProxyDir, [%doctrine.proxy_dir.path%] ]
          - [ setProxyNamespace, [%doctrine.proxy.namespace%] ]
          - [ setAutoGenerateProxyClasses, [%debug%] ]

    em:
        class: %doctrine_entity_manager.class%
        factory_class: %doctrine_entity_manager_factory.class%
        factory_method: create
        arguments:
          - %doctrine.connection.config%
          - @doctrine_configuration

    doctrine:
        alias: em