I am currently building a package for ConcreteCMS to give users an access to an invoice list.

I use this Doctrine entity to store invoices:

/**
 *  @Entity
 * @Table(name="CommunityStoreSi3bEcommerceUserInvoices")
 */
class UserInvoice {
    /**
     * @Id
     * @Column(type="integer")
     * @GeneratedValue
     */
    protected ?int $id;

    /**
     * @ManyToOne(targetEntity="ConcreteCoreUserUser", nullable=false)
     */
    protected ?User $user;

    /**
     * @Column(nullable=true)
     * @ManyToOne(targetEntity="ConcretePackageCommunityStoreSrcCommunityStoreOrderOrder")
     */
    protected ?Order $order;

    /**
     * @Column(type="text", nullable=false)
     */
    protected ?string $invoice_uid;

    /**
     * @Column(type="datetime", nullable=false)
     */
    protected ?DateTime $created_at;

And on my controller, I do this to get invoices from the current user:

$invoices = $em->getRepository(UserInvoice::class)->findBy(['user' => $u]);

With $u being an instance of ConcreteCoreUserUser. Yet, I get this error message from Doctrine:

An exception occurred while executing 'SELECT t0.id AS id_1, t0.user AS user_2, t0.order AS order_3, t0.invoice_uuid AS invoice_uuid_4, t0.created_at AS created_at_5 FROM CommunityStoreSi3bEcommerceUserInvoices t0 WHERE t0.user = ?' with params [{"error":"","uID":2,"uName":"QuentinD","uGroups":{"2":2,"3":3,"1":1},"superUser":false,"uTimezone":null}]: Object of class ConcreteCoreUserUser could not be converted to string

Trying to work around this with findBy(['user' => $u->getUserID()]) I get a TypeError Cannot assign string to property UserInvoice::$user of type ?ConcreteCoreUserUser.

Do you have any idea why ?