Adding different item types to cart.

ItemResolver.php

<?php

namespace App\Bundle\AppBundle\Resolver;

use Doctrine\Common\Persistence\ObjectRepository;
use Sylius\Bundle\CartBundle\Model\CartItemInterface;
use Sylius\Bundle\CartBundle\Resolver\ItemResolverInterface;
use Sylius\Bundle\CartBundle\Resolver\ItemResolvingException;
use Symfony\Component\HttpFoundation\Request;

class CartItemResolver implements ItemResolverInterface
{
    private $productRepository;
    private $packageRepository;

    public function __construct(ObjectRepository $productRepository, ObjectRepository $packageRepository)
    {
        $this->productRepository = $productRepository;
        $this->packageRepository = $packageRepository;
    }

    public function resolve(CartItemInterface $item, Request $request)
    {
        if (null !== $productId = $request->get('productId')) {
            return $this->resolveProduct($productId, $item, $request);
        }

        if (null !== $packageId = $request->get('packageId')) {
            return $this->resolvePackage($packageId, $item, $request);
        }

        throw new ItemResolvingException('Error occured while adding item to cart');
    }

    private function resolveProduct($id, CartItemInterface $item, Request $request)
    {
        if (!$product = $this->productRepository->find($id)) {
            throw new ItemResolvingException('Requested product is not available');
        }

        $item->setProduct($product);
        $item->setUnitPrice($product->getRetailPrice());

        return $item;
    }

    private function resolvePackage($id, CartItemInterface $item, Request $request)
    {
        if (!$package = $this->packageRepository->find($id)) {
            throw new ItemResolvingException('Requested package is not available');
        }

        $item->setPackage($package);
        $item->setUnitPrice($package->getRetailPrice());

        return $item;
    }
}