API Platform itemOperation with multiple identifiers

CartSku.php

<?php

namespace App\Doctrine\Entity;

use ApiPlatform\Core\Action\NotFoundAction;
use ApiPlatform\Core\Action\PlaceholderAction;
use ApiPlatform\Core\Annotation\ApiProperty;
use ApiPlatform\Core\Annotation\ApiResource;
use App\Coupon\Model\OrderSkuInterface;
use App\Doctrine\Validator\Constraints\CartSkuLoyalty;
use App\Doctrine\Validator\Constraints\CartSkuQty;
use App\Util\Price;
use Doctrine\ORM\Mapping as ORM;
use Gedmo\IpTraceable\Traits\IpTraceableEntity;
use Gedmo\Timestampable\Traits\TimestampableEntity;
use Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntity;
use Symfony\Component\Serializer\Annotation\Groups;
use Symfony\Component\Validator\Constraints as Assert;

/**
 * @ORM\Entity
 * @ApiResource(
 *     normalizationContext={"groups"={"cartSku:read"}},
 *     denormalizationContext={"groups"={"cartSku:write"}},
 *     collectionOperations={
 *          "get"={"controller"=NotFoundAction::class}
 *     },
 *     itemOperations={
 *          "get" = {
 *              "method"="GET",
 *              "path"="/cart/sku/{cart}/{sku}.{_format}",
 *              "swagger_context" = {
 *                  "summary"="Get sku qty in current cart"
 *              }
 *          
 *     }
 * )
 */
class CartSku
{
    /**
     * @var Cart
     *
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="NONE")
     * @ORM\ManyToOne(targetEntity="App\Doctrine\Entity\Cart", inversedBy="cartSkus")
     *
     * @ApiProperty(identifier=true)
     */
    private $cart;

    /**
     * @var Sku
     *
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="NONE")
     * @ORM\ManyToOne(targetEntity="App\Doctrine\Entity\Sku")
     *
     * @ApiProperty(identifier=true, attributes={"fetchEager": true})
     */
    private $sku;
}

CartSkuSubscriber.php

<?php

namespace App\Doctrine\EventSubscriber;

use ApiPlatform\Core\EventListener\EventPriorities;
use App\Doctrine\Entity\Cart;
use App\Doctrine\Entity\CartSku;
use App\Doctrine\Entity\Sku;
use Doctrine\ORM\EntityManagerInterface;
use Doctrine\ORM\EntityNotFoundException;
use Doctrine\ORM\ORMException;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\Event\RequestEvent;
use Symfony\Component\HttpKernel\Event\ViewEvent;
use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
use Symfony\Component\HttpKernel\KernelEvents;

class CartSkuSubscriber implements EventSubscriberInterface
{
    /**
     * @var EntityManagerInterface
     */
    private $entityManager;

    public function __construct(EntityManagerInterface $entityManager)
    {
        $this->entityManager = $entityManager;
    }

    /**
     * @return array
     */
    public static function getSubscribedEvents()
    {
        return [
            KernelEvents::REQUEST => ['onPreRead', EventPriorities::PRE_READ],
            KernelEvents::VIEW => ['onPreValidate', EventPriorities::PRE_VALIDATE],
        ];
    }

    public function onPreRead(RequestEvent $event)
    {
        $attributes = $event->getRequest()->attributes;
        $loyaltySku = null;

        if (CartSku::class !== $attributes->get('_api_resource_class')) {
            return;
        }

        $idApiP = [
            'sku' => $event->getRequest()->attributes->get('sku', $loyaltySku),
            'cart' => $event->getRequest()->attributes->get('cart'),
        ];

        $event->getRequest()->attributes->add($idApiP);
        $event->getRequest()->attributes->set('id', http_build_query($idApiP, '', ';'));
    }

    /**
     * @throws ORMException
     */
    public function onPreValidate(ViewEvent $event)
    {
        $cartSku = $event->getControllerResult();

        if (!$cartSku instanceof CartSku) {
            return;
        }

        $attributes = $event->getRequest()->attributes;

        try {
            /** @var Sku $sku */
            $sku = $this->entityManager->getReference(Sku::class, $attributes->get('sku'));
            /** @var Cart $cart */
            $cart = $this->entityManager->getReference(Cart::class, $attributes->get('cart'));

            $cartSku->setCart($cart);
            $cartSku->setSku($sku);

        } catch (EntityNotFoundException $e) {
            throw new NotFoundHttpException($e->getMessage(), $e);
        }
    }
}