2 of one fields valid

Apicontroller.php

<?php
namespace AppBundle\Controller;

...

class ApiController extends Controller
{

    /**
     * @Route("...")
     * @Method("POST")
     */
    public function postFilesAction(Request $request)
    {
        $validator = $this->get('validator');
        $requestCredentials = PostRequestCredentials::fromRequest($request, $this->getParameter('max_filesize'));
        $errors = $validator->validate($requestCredentials);

        if (count($errors) !== 0) {
            return $this->processAndReturnErrors($errors);
        }
        
        ...
     }
     
     ...
     
}     

PostRequestCredentials.php

<?php

namespace AppBundle\RequestCredentials;


use Symfony\Component\HttpFoundation\File\File;
use Symfony\Component\HttpFoundation\File\UploadedFile;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\Validator\Constraints as Assert;
use Symfony\Component\Validator\Context\ExecutionContextInterface;
use Symfony\Component\Validator\Mapping\ClassMetadata;


class PostRequestCredentials
{

    const FILES_POST_USER_ID_BLANK = 2;
    const FILES_POST_FILE_TOO_BIG = 3;
    const FILES_POST_FILE_NOT_IMAGE = 4;
    const FILES_POST_CREATION_THROUGH_URL_ERROR = 5;    


    public static $maxFilesize;

    /**
     * @Assert\NotBlank(payload = {"error_code" = "2"}, message="user_id mustn't be blank")
     * @Assert\Type(type="digit", payload = {"error_code" = "2"}, message="user_id mustn't be blank")
     * @Assert\Range(min = 1, minMessage="user_id must be more than zero", invalidMessage="user_id must be a positive integer")
     */
    private $userId;

    private $file;

    /**
     * @Assert\Url(payload = {"error_code" = "5"})
     */
    private $fileUrl;


    public static function fromRequest(Request $request, $maxFilesize)
    {
        $instance = new self;
        $instance->userId = $request->get('user_id');
        $instance->file = $request->files->get('file');
        $instance->fileUrl = $request->get('file_url');
        self::$maxFilesize = $maxFilesize;
        return $instance;
    }

    /**
     * @Assert\Callback()
     */
    public function validate(ExecutionContextInterface $context)
    {
        if (! ($this->fileExistsAndValid() || $this->fileUrlExistsAndValid())) {
            $context->buildViolation('Neither file nor file_url is present.')->addViolation();
        }
    }

    private function fileExistsAndValid()
    {
        return isset($this->file) && ($this->file instanceof UploadedFile);
    }

    private function fileUrlExistsAndValid()
    {
        return isset($this->fileUrl) && ($this->fileUrl);
    }

    /**
     * @return integer
     */
    public function getUserId()
    {
        return $this->userId;
    }

    /**
     * @return File | null
     */
    public function getFile()
    {
        return $this->file;
    }

    /**
     * @return string
     */
    public function getFileUrl()
    {
        return $this->fileUrl;
    }

}