Symfony 2 Sonata Media bundle: saving media file image without sonata admin

I have using the Sonata Admin Bundle and Sonata Media Bundle. It's great, but i have the problem about using Media. https://sonata-project.org/bundles/media/2-2/doc/index.html

Example I have a Post Document, in Post I have $image variable with targetDocument is Media. And When I create new Post, I must upload the image file, and before save Post, I must save the upload image file to Media Entity first and then I pointing the $image of Post to the Media Entity just been saved.

Post Document:

<?php
namespace Acme\Bundle\PostBundle\Document;

use Doctrine\ODM\MongoDB\Mapping\Annotations as MongoDB;
use Symfony\Component\Validator\Constraints as Assert;

/**
 * @MongoDB\Document(repositoryClass="Acme\Bundle\PostBundle\Repository\PostRepository")
 */
class Post
{
    /**
     * @MongoDB\Id
     */
    protected $id;

    /**
     * @MongoDB\String
     */
    protected $name;

    /**
     * @MongoDB\ReferenceOne(targetDocument="Application\Sonata\MediaBundle\Document\Media", nullable=true )
     */
    protected $image;

Can we have any way to access the Media Entity and save the upload file to it in Post Document function. I had read this but it not help more.

https://sonata-project.org/bundles/media/master/doc/reference/form.html

The answer is here:

In above code, we must save the upload image to media first and then pointed it to the post:

    $mediaManager = $this->container->get('sonata.media.manager.media');
    $media = new Media();
    $media->setBinaryContent($uploadImage);
    $media->setContext('default');
    $media->setProviderName('sonata.media.provider.image');
    $mediaManager->save($media);
    $post->setImage($media);
    print_r($media);exit;