Retrieve session value and pass to an entity attribute - symfony

Question

I want to retrieve a quantity for each item that I store in session and store it in database.
How do I retrieve the quantity in session and passed to my quantity attribute of my article entity during database persistence?
For example for this article:
(id 4, quantity 2).
I would store 2 in the quantity attribute of my article entity.
I tried :
$article->setQuantity($session->get('panier'));
I have this error:
An exception occurred while executing 'INSERT INTO article ....... {"4": "2"}
Notice: Array to string conversion
/**
* #Route("/payment", name="payment")
*/
public function paymentAction(Request $request)
{
$session = $request->getSession();
$produits = $this->getDoctrine()->getManager()->getRepository('AppBundle:Stock')->findArray(array_keys($session->get('panier')));
$commande = $session->get('commande');
var_dump($session->get('panier'));
if ($request->isMethod('POST')) {
$token = $request->get('stripeToken');
\Stripe\Stripe::setApiKey($this->getParameter("private_key"));
\Stripe\Charge::create(array(
"amount" => $commande->getTotal() * 100,
"currency" => "EUR",
"source" => $token,
"description" => ""
));
foreach ($produits as $produit) {
$article = new Article();
$article->setTitle($produit->getStock()->getTitle());
$article->setContent($produit->getStock()->getContent());
//problem here
$article->setQuantity($session->get('panier'));
//
$article->setPrice($produit->getPrice());
$commande->addArticle($article);
$em = $this->getDoctrine()->getManager();
$em->persist($commande);
$em->flush();
}
return $this->redirectToRoute('confirmation');
}
return $this->render(':default:payment.html.twig', array(
'commande' => $commande,
'panier' => $session->get('panier'),
'produits' => $produits,
'public_key' => $this->getParameter("public_key"),
));
}
Add article in session :
/**
* #Route("/shop/add/{id}", name="add_article")
*
*/
public function addArticlelAction(Request $request, $id)
{
$session = $request->getSession();
if (!$session->has('panier'))
$session->set('panier', array());
$panier = $session->get('panier');
if (array_key_exists($id, $panier)) {
if ($request->query->get('qte') != null)
$panier[$id] = $request->query->get('qte');
} else {
if ($request->query->get('qte') != null)
$panier[$id] = $request->query->get('qte');
else
$panier[$id] = 1;
}
$session->set('panier', $panier);
return $this->redirectToRoute('panier');
}

Answer 1

UPDATE:
If $id in addArticlelAction is the product id then:
foreach ($produits as $produit) {
$article = new Article();
$article->setTitle($produit->getStock()->getTitle());
$article->setContent($produit->getStock()->getContent());
//problem here
$article->setQuantity($session->get('panier')[$produit->getId()]);
//
$article->setPrice($produit->getPrice());
$commande->addArticle($article);
$em = $this->getDoctrine()->getManager();
$em->persist($commande);
$em->flush();
}
should work, because for the moment you have two products (product1 who has id 1 and product 4 who has id 4). When you call /shop/add/{id}, you are adding to $session->get('panier')[1] and $session->get('panier')[4] the quantities. So, when you're in foreach (to store in DB), you need to access index 1 and index 4 ($produit->getId())