Symfony2: Form CheckboxType management with Domain object

AcmeDemoType.php

<?php

namespace Acme\Bundle\DemoBundle\Form\Type;

use Acme\Bundle\DemoBundle\Domain\DemoDomain;
use Acme\Bundle\DemoBundle\Entity\Demo;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;

class DemoType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('name', 'text', array(
                'property_path' => 'demo.name',
            ))
            ->add('regenerateApiKey', 'checkbox', array(
                'required' => false,
            ))
            ->add('save', 'submit');
    }

    public function setDefaultOptions(OptionsResolverInterface $resolver)
    {
        $resolver->setDefaults(array(
            'data_class' => 'Acme\Bundle\DemoBundle\Domain\DemoDomain',
            'empty_data' => new DemoDomain(new Demo()),
        ));
    }

    public function getName()
    {
        return 'acme_demo';
    }
}

Demo.php

<?php

namespace Acme\Bundle\DemoBundle\Entity;

use Doctrine\ORM\Mapping as ORM;
use Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntity;
use Symfony\Component\Validator\Constraints as Assert;

/**
 * @ORM\Entity
 * @ORM\Table(name="demo")
 * @UniqueEntity(fields={"name"}, errorPath="name", message="The name already exists.")
 */
class Demo
{
    /**
     * @ORM\Id
     * @ORM\Column(type="integer")
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    protected $id;

    /**
     * @ORM\Column(type="string", length=20, unique=true)
     * @Assert\NotBlank
     * @Assert\Length(max=20)
     */
    protected $name;

    /**
     * @ORM\Column(name="api_key", type="string", length=50, nullable=true)
     * @Assert\Length(max=50)
     */
    protected $apiKey;

    public function getId()
    {
        return $this->id;
    }

    public function getName()
    {
        return $this->name;
    }

    public function setName($name)
    {
        $this->name = $name;
    }

    public function getApiKey()
    {
        return $this->apiKey;
    }

    public function setApiKey($apiKey)
    {
        $this->apiKey = $apiKey;
    }

    public function regenerateApiKey()
    {
        $this->setApiKey(base_convert(sha1(uniqid(mt_rand(), true)), 16, 36));
    }
}

DemoController.php

<?php

namespace Acme\Bundle\DemoBundle\Controller;

use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\HttpFoundation\Request;

class DemoController extends Controller
{
    public function createAction(Request $request)
    {
        $form = $this->createForm('acme_demo');

        if ($request->isMethod('POST')) {
            $form->bind($request);

            if ($form->isValid()) {
                $demoDomain = $form->getData();

                $demoDomain->save();
                $demo = $demoDomain->getDemo();

                $em = $this->getEntityManager();
                $em->persist($demo);
                $em->flush();

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

        return $this->render('AcmeDemoBundle:Demo:edit.html.twig', array(
            'form' => $form->createView(),
        ));
    }

    protected function getRepository()
    {
        return $this->getEntityManager()->getRepository('AcmeDemoBundle:Demo');
    }

    protected function getEntityManager()
    {
        return $this->container->get('doctrine')->getManagerForClass('AcmeDemoBundle:Demo');
    }
}

DemoDomain.php

<?php

namespace Acme\Bundle\DemoBundle\Domain;

use Acme\Bundle\DemoBundle\Entity\Demo;
use Symfony\Component\Validator\Constraints as Assert;

class DemoDomain
{
    /**
     * @Assert\Type("bool")
     */
    public $regenerateApiKey;

    /**
     * @Assert\Valid
     */
    protected $demo;

    public function __construct(Demo $demo)
    {
        $this->demo = $demo;
        $this->regenerateApiKey = false;
    }

    public function getDemo()
    {
        return $this->demo;
    }

    public function save()
    {
        if ($this->regenerateApiKey) {
            $this->demo->regenerateApiKey();
        }
    }
}