扩展实体中的验证不起作用

I have an Entity Media which have protected File value

<?php

namespace Chiave\MediaBundle\Entity;

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

/**
 * @ORM\Table(name="media")
 * @ORM\Entity
 * @ORM\HasLifecycleCallbacks
 */
class Media
{


...

/**
     * @Assert\File(
     *     maxSize="5M"
     * )
     */
    protected $file;

Then i extend this class in my AppBundle because I need only images to get pass validation

<?php

namespace AppBundle\Entity;

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

/**
 * @ORM\Entity
 * @ORM\Table(name="image")
 */
class Image extends \Chiave\MediaBundle\Entity\Media
{
    /**
     * @Assert\Image()
     */
    protected $file;
}

Also i have Form Type for this which looks like this

<?php

namespace AppBundle\Form;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;
use AppBundle\Form\ImageType as ImageType;

class POIType extends AbstractType
{

    /**
     * @param FormBuilderInterface $builder
     * @param array                $options
     */
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
                ...
                ->add('images', 'collection', [
                    'type' => new ImageType,
                    'allow_add' => true,
                    'allow_delete' => true,
                    'by_reference' => false,
                    'label' => ' ',
                ]);
    }

My problem is that validation didn`t work. I can upload image yes, but i can also upload PHP file or... pretty much everything. Any ideas? I will be very grateful.

Thanks in advance.

You don't have extend Media Entity. You can use constraints directly in your form builder like that :

$builder
            ->add('images', 'collection', [
                'type' => new ImageType,
                'allow_add' => true,
                'allow_delete' => true,
                'by_reference' => false,
                'label' => ' ',
                'constraints' = new Image(array(
                    'minWidth' => 200,
                    'maxWidth' => 400,
                    'minHeight' => 200,
                    'maxHeight' => 400,
                ))
            ]);

Don't forget to import Image Constraint Class:

use Symfony\Component\Validator\Constraints\Image