Symfony 3.4/Doctrine 2 one-to-one association error - php

Question

I have two entities - User and Cart. They're supposed to have a one-to-one association, created by the following:
User.php:
namespace AppBundle\Entity;
use FOS\UserBundle\Model\User as BaseUser;
use Doctrine\ORM\Mapping as ORM;
use Doctrine\Common\Collections\ArrayCollection;
use Symfony\Component\Validator\Constraints as Assert;
/**
* #ORM\Entity
* #ORM\Table(name="fos_user")
*/
class User extends BaseUser
{
/**
* #ORM\OneToOne(targetEntity="Cart", mappedBy="user")
*/
private $cart;
// other things not related to the association
}
Cart.php:
namespace AppBundle\Entity;
use Doctrine\ORM\Mapping as ORM;
use Doctrine\Common\Collections\ArrayCollection;
/**
* Class Cart
* #package AppBundle\Entity
*
* #ORM\Entity
* #ORM\Table(name="Cart")
*/
class Cart
{
/**
* #ORM\OneToOne(targetEntity="User", inversedBy="cart")
*/
private $user;
// other things not related to the association
}
I create the cart and persist all entities when someone attempts to view their cart for the first time:
CartController.php:
public function showCartAction()
{
$this->denyAccessUnlessGranted('IS_AUTHENTICATED_FULLY');
$user = $this->getUser();
$cart = $user->getCart();
if ($cart) {
$items = $cart->getCartItems();
} else {
$cart = new Cart();
$user->setCart($cart);
$em = $this->getDoctrine()->getManager();
$em->persist($cart);
$em->persist($user);
$em->flush();
$items = $cart->getCartItems();
}
// other unrelated things in the controller
}
With this, carts are created, but there's no association between User and Cart:
user_id should have the user's id.
Any ideas on why this isn't working? And is it possible to simply do something like:
public function __construct()
{
$this->cart = new Cart();
}
In my User entity? Would that enforce the association? Or is that the wrong way to go?

Answer 1

You probably want to ensure that a cart can not bet created without a user being associated with it. Unlike fields, associations are nullable by default. You have to add a JoinColumn annotation for this.
/**
* #ORM\OneToOne(targetEntity="User", inversedBy="cart")
* #ORM\JoinColumn(nullable=false)
*/
private $user;
The other thing is that since you have a bi-directional association you have to make sure that when calling $user->setCart($cart) this will also add the user to the cart, e.g. like this:
public function setCart(Cart $cart): void
{
$this->cart = $cart;
$cart->setUser($this);
}
Since the cart can not be created without a user you could also make the user a constructor argument instead:
public function __construct(User $user)
{
$this->user = $user;
$user->setCart($this);
}
This way you can omit the setUser() method on the cart ensuring that no one switches the cart owner by accident.
With the latter one you might not even have to link back to the user, since the cart is the owning side, but to ensure that both entities have a consistent state I would always do this, when you have a bi-directional association.