Symfony2 fetch data from entity with OneToMany relation

I have two entities: Ad and AdPhoto. They have relation: OneToMany(Many AdPhoto to one Ad). After persist, I tried to get AdPhoto from Ad by method Ad::getPhoto(), but I get PersistentCollection class and I dont know what do with it.

Help me to understand how I can get all related AdPhoto to Ad.

Entity Ad:

namespace AdBundle\Entity;

use Doctrine\Common\Collections\ArrayCollection;
use Doctrine\ORM\Mapping as ORM;

/**
 * Ad
 *
 * @ORM\Table(name="Ad")
 * @ORM\Entity
 */
class Ad
{
...
    /**
     * @ORM\OneToMany(targetEntity="AdBundle\Entity\AdPhoto", mappedBy="id")
     */
    private $photo;
...
}

Entity AdPhoto:

namespace AdBundle\Entity;

use Doctrine\ORM\Mapping as ORM;
use Symfony\Component\HttpFoundation\File\UploadedFile;
use Symfony\Component\Validator\Constraints as Assert;

/**
 * AdPhoto
 *
 * @ORM\Table(name="AdPhoto")
 * @ORM\Entity
 */
class AdPhoto
{
    ...    
    /**
     * @ORM\ManyToOne(targetEntity="AdBundle\Entity\Ad", inversedBy="photo")
     * @ORM\JoinColumn(name="ad", referencedColumnName="id")
     */
    private $ad;
...
}

In controller:

$ad = $this->getDoctrine()->getRepository('AdBundle:Ad')
            ->findOneBy(array(
                'id' => $id
            ));

        var_dump($ad->getPhoto());

        return $this->render('AdBundle:Default:view.html.twig', array(
            'ad' => $ad
        ));

You can loop through array collection in twig like through regular array. If you want to use it as array in php code you can use

$photos = $ad->getPhotos()->toArray();

And since add can have many photos it would be better to use $photos instead $photo.