protected function overrideAlternative(FormInterface $form)
    {
        $needFlush = false;
        foreach ($this->thumbnailConfig as $format => $parameters) {
            $file = $form->get('files')->get($format)->get('file')->getData();
            if (null !== $file) {
                $media = $form->getData();
                $tmpFileName = time() . '-' . $file->getClientOriginalName();
                $file->move($this->tmpDir, $tmpFileName);
                $tmpFilePath = $this->tmpDir . DIRECTORY_SEPARATOR . $tmpFileName;
                $this->imageAlternativeStrategy->overrideAlternative($media, $tmpFilePath, $format);
               $this->objectManager->persist($media);
                $needFlush = true;
            }
        }
        if ($needFlush) {
            $this->objectManager->flush();
        }
    }