How to set a default value in a Symfony 2 form field?
class QuotesType extends AbstractType
{
    private $id;

    public function __construct($id){
        $this->product_id = $id;
    }

    public function buildForm(FormBuilder $builder, array $options)
    {
        $builder
            ->add('user_name',              'text')
            ->add('user_lastname',          'text')
            ->add('user_email',             'email')
            ->add('user_comments',          'textarea')
            ->add('user_product_id',        'hidden', array(
                'data' => $this->product_id,
            ));
        ;
    }

namespace QNMainBundleEntity;

use DoctrineORMMapping as ORM;
use SymfonyComponentValidatorConstraints as Assert;

/**
 * QNMainBundleEntityQuotes
 *
 * @ORMTable()
 * @ORMEntity(repositoryClass="QNMainBundleEntityQuotesRepository")
 */
class Quotes
{

    public function __construct($p_id)
    {
        $this->date = new Datetime('today');
    }
    /**
     * @var integer $id
     *
     * @ORMColumn(name="id", type="integer")
     * @ORMId
     * @ORMGeneratedValue(strategy="AUTO")
     */
    private $id;

    /**
     * @var integer $user_product_id
     *
     * @ORMColumn(name="user_product_id", type="integer")
     */
    private $user_product_id = "1";

    /**
     * @var datetime $date
     *
     * @ORMColumn(name="date", type="datetime")
     */
    private $date;

public function requestAction($id)
    {
        $repository = $this->getDoctrine()
                           ->getEntityManager()
                           ->getRepository('QNMainBundle:Categories');
    $categories = $repository->findAll();

    $quote = new Quotes($id);
    $form = $this->createForm(new QuotesType(), $quote);

    $formHandler = new QuotesHandler($form, $this->get('request'), $this->getDoctrine()->getEntityManager());

    if( $formHandler->process() )
    {
        return $this->redirect( $this->generateUrl('QNMain_Product', array('id' => $id)) );
    }

    return $this->render('QNMainBundle:Main:requestaform.html.twig', array(
        'categories' => $categories,
        'id' => $id,
        'form' => $form->createView(),
    ));

}

namespace QNMainBundleForm;

use SymfonyComponentFormForm;
use SymfonyComponentHttpFoundationRequest;
use DoctrineORMEntityManager;
use QNMainBundleEntityQuotes;

class QuotesHandler
{
    protected $form;
    protected $request;
    protected $em;

    public function __construct(Form $form, Request $request, EntityManager $em)
    {
        $this->form    = $form;
        $this->request = $request;
        $this->em      = $em;
    }

    public function process()
    {
        if( $this->request->getMethod() == 'POST' )
        {
            $this->form->bindRequest($this->request);

            if( $this->form->isValid() )
            {
                $this->onSuccess($this->form->getData());

                return true;
            }
        }

        return false;
    }

    public function onSuccess(Quotes $quote)
    {
        $this->em->persist($quote);
        $this->em->flush();
    }

}

/**
 * @ORMAnnotations...
 */
private $user_product_id = 9000;