EntityManagerInterface in Controllers vs Services

[vitoff34]

Hello,
I am trying to build a Cart functionality for my website.
I want to implement this code in a service:

public function addItem($product, $quantity = 1)
    {
        $cart = $this->getCart();

        $productEntity = $this->entityManager->getRepository(Product::class)->find($product);
        $cartEntity = $this->entityManager->getRepository(Order::class)->find($cart->getId());
        $orderItem = $this->entityManager->getRepository(OrderItem::class)->findOneBy(['product' => $productEntity, 'orderId' => $cartEntity]);

        if (!$orderItem instanceof OrderItem)
        {
            $orderItem = new OrderItem();
            $orderItem->setQuantity(1);
            $orderItem->setProduct($productEntity);
            $orderItem->setOrderId($cart);

            $this->entityManager->persist($orderItem);
        } else
        {
            $orderItem->setQuantity($orderItem->getQuantity() + $quantity);
        }

        return [
            'cart' => $cart,
            'totalItems' => $this->getCartTotalItems()
        ];
    }

public function getCart()
    {
        $cart = $this->session->get('cart', []);

        if (!$cart)
        {
            $cart = new Order();
            $cart->setStatus(Order::STATUS_CART);

            if ($this->security->getUser())
            {
                $cart->setUser($this->security->getUser());
            }

            $this->entityManager->persist($cart);
            $this->entityManager->flush();

            $this->session->set('cart', $cart);
        }
        return $cart;
    }

However I get these type of errors :
Multiple non-persisted new entities were found through the given association graph
There are for different entities which do not have any relation to this operation.
When I do it in a Controller it works just fine.
This is my service definition:

 cart_service:
        class: App\Service\CartService
        arguments:
            - '@doctrine.orm.entity_manager'
            - '@Symfony\Component\HttpFoundation\Session\SessionInterface'
            - '@security.token_storage'

These are my relationships:
Order:

#[ORM\OneToMany(targetEntity: OrderItem::class, mappedBy: 'orderId', cascade: ['persist'])]
    private Collection $orderItems;
OrderItem:
 #[ORM\ManyToOne(inversedBy: 'orderItems', cascade: ['persist'])]
    #[ORM\JoinColumn(nullable: true)]
    private ?Order $orderId = null;
#[ORM\ManyToOne(inversedBy: 'orderItems')]
    private ?Product $product = null;

Any help would be much appreciated. Thanks :)

[stof]

the issue is that getCart returns an Order object coming from the session, which won't be managed by the ORM. You should be using $orderItem->setOrderId($cartEntity);

[vitoff34]

Thank you very much!