Sonata - Implement a form inside the show template

Question

I need to implement a form inside my show template of a specific admin. In the original demo of Symfony a great example is shown. Please take a look at it here;

1. Controller (look at the method on line 120 as well)
2. Post Show template
3. Comment Form template

---

Now what I've done in Sonata;

I've created the custom CRUD Controller for the specific admin class (OrderAdmin). I already have a clone action there that works well, so I know my custom CRUD Controller works perfect.

I also have a custom show template specific for OrderAdmin. Again that works well, because I already have something custom there.

Now for my work relating to this custom comment form;

My action just to render the form (like in the Symfony demo):

/**
 * @param Order $order
 * @return \Symfony\Component\HttpFoundation\Response
 */
public function commentFormAction(Order $order)
{
    $form = $this->createFormBuilder()
        ->add('comment')
        ->getForm();

    return $this->render('AppBundle:Order:_comment_form.html.twig', array(
        'order' => $order,
        'form' => $form->createView(),
    ));
}

A snippet of my show template:

<div class="row">
        <div class="col-md-12">
            {{ render(controller('AppBundle:OrderCRUD:commentForm', { 'id': object.id })) }}
        </div>
    </div>

and finally my _comment_form template where the form self is rendered:

{{ form_start(form) }}
    {{ form_widget(form) }}
    <button class="btn btn-primary pull-right" type="submit">Comment</button>
{{ form_end(form) }}

I'm pretty sure this is all setup fine, the only problem I get is that...

An exception has been thrown during the rendering of a template ("There is no _sonata_admin defined for the controller AppBundle\Controller\OrderCRUDController and the current route ``").

I have another action that will be the comment form action, but I get the problem here before that action is called on form submission.

Can somebody please help me understand this _sonata_admin. How do I define it? What should I had to my code, or how do I have to change it to get a form function properly in my show template. Does anybody have an example of how to accomplish this? I've come across a few posts over the web where people struggle with this.

I've also started a bounty on this question with a very very similar issue.

I desperately need help to get this to work. Please? I know Sonata support is quite poor but I need you guys, please.