AlbumRepository is a solo class

No Doctrine getRepository() magic. Sometimes you need more than a single repository. When you need more complex queries in repository you may create standard Doctrine repository that extends EntityRepository (see http://docs.doctrine-project.org/en/2.0.x/reference/working-with-objects.html#custom-repositories). The problem is that you cannot inject any other services into standard Doctrine repositories.

As a result its much better (in sustainable in the long run) to create your own Doctrine repositories which does not extend any base class. In this case you can inject them with any service you need.