Use ClassMetadata as a service

services.yml

services:
    # Use an entity's ClassMetadata as if it where a service (for example, in
    # other services definitions).
    #
    # See http://symfony.com/doc/2.0/components/dependency_injection/factories.html
    foo.foo_class_metadata:
        class: "Doctrine\\Common\\Persistence\\Mapping\\ClassMetadata"
        factory_service: doctrine.orm.entity_manager
        factory_method: getClassMetadata
        arguments:
            # Fully-qualified entity class name
            - "Foo\\Bundle\\FooBundle\\Entity\\Foo"