Where to place business logic in Symfony2?

After reading a lot of posts and Stack Overflow resources, I've still got some problems about the famous question about "where to put business logic?" Reading StackOverflow Question and A Blog Post, I believe I've understood the issue of code separation well.

Suppose I have a web form where you can add a user that will be added to a db. This example involves these concepts:

• Form
• Controller
• Entity
• Service
• Repository

If I didn't miss something, you have to create an entity with some properties, getters, setters and so on in order to make it persist into a db. If you want to fetch or write that entity, you'll use entityManager and, for "non-canonical" query, entityRepository (that is where you can fit your "query language" query).

Now you have to define a service (that is a PHP class with a "lazy" instance) for all business logic; this is the place to put "heavy" code. Once you've recorded the service into your application, you can use it almost everywhere and that involves code reuse and so on.

When you render and post a form, you bind it with your entity (and with constraints of course) and use all the concepts defined above to put all together.

So, "old-me" would write a controller's action in this way:

public function indexAction(Request $request)
    {
        $modified = False;
        if($request->getMethod() == 'POST'){ // submit, so have to modify data
            $em = $this->getDoctrine()->getEntityManager();
            $parameters = $request->request->get('User'); //form retriving
            $id = $parameters['id'];
            $user = $em->getRepository('SestanteUserBundle:User')->find($id);