File.php

<?php

/**
 * @Assert\Callback(methods={"validateFile"})
 */
class File
{
    public function validateFile(ExecutionContext $context)
    {
        if (null !== $this->getId()) {
            return;
        }

        $context->setPropertyPath($context->getPropertyPath().'.file');
        
        $validator = new NotBlankValidator();
        $validator->initialize($context);
        $validator->validate($this->getFile(), new NotBlank());
    }
}