Base form code for saving multiple classes of data with Symfony2. This is for Jerome.

CommentType.php

<?php

namespace Your\Product\Bundle\Form\CommentType;

use Your\Product\Bundle\Form\UserType;

class CommentType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('comment', 'textarea', array(
                'label' => 'Comments'
            ))
            ->add('user', new UserType(), array(
                'data_class' => 'Your\Product\Bundle\Entity\User',
            ))
        ;
    }

    // ....
}  

ProductController.php

<?php

namespace Your\Product\Bundle\Controller\ProductController;

use Your\Product\Bundle\Entity\Comment;
use Your\Product\Bundle\Form\CommentType;

class ProductController extends Controller
{
    /**
     * Show the Product and display the Comment form
     *
     * @Route("/{id}/product", name="product")
     * @Method("GET")
     * @Template()
     */
    public function productAction($id)
    {
        $em = $this->getDoctrine()->getManager();

        $product = $em->getRepository('YourProductBundle:Product')->find($id);

        if (!$product) {
            throw $this->createNotFoundException('Unable to find Product entity.');
        }

        $comment = new Comment;
        $comment->addProduct($product);
        $commentForm = $this->createForm(new CommentType(), $comment);

        return array(
            'product'      => $product,
            'comment_form' => $commentForm->createView()
        );
    }

    /**
     * Adds a comment to a product
     *
     * @Route("/{id}/product/comment", name="product_add_comment")
     * @Method("PUT")
     * @Template("YourProductBundle:Product:product.html.twig")
     */
    public function updateAction(Request $request, $id)
    {
        $em = $this->getDoctrine()->getManager();

        $product = $em->getRepository('YourProductBundle:Product')->find($id);

        if (!$product) {
            throw $this->createNotFoundException('Unable to find Product entity.');
        }

        $comment = new Comment;
        $comment->addProduct($product);
        $commentForm = $this->createForm(new CommentType(), $comment);

        $commentForm->bind($request);

        if ($commentForm->isValid()) {
            $em->persist($comment);
            $em->flush();

            return $this->redirect($this->generateUrl('product', array('id' => $id)));
        }

        return array(
            'product'      => $product,
            'comment_form' => $commentForm->createView()
        );
    }

}

UserType.php

<?php

namespace Your\Product\Bundle\Form\UserType;

class UserType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('name', 'text', array(
                'label' => 'Name'
            ))
            ->add('email', 'email', array(
                'label' => 'Email Address'
            ))
        ;
    }

    // ....
}