表单不在Symfony 4中呈现OneToMany关系的字段

// src/Entity/User.php

use Doctrine\Common\Collections\ArrayCollection;
use Doctrine\Common\Collections\Collection;

class User
{
    // ...

    /**
     * @ORM\OneToMany(targetEntity="App\Entity\Comment", mappedBy="user")
     */
    private $comments;

    public function __construct()
    {
        $this->comments = new ArrayCollection();
    }

    // ...
}

// src/Form/UserType.php

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\Extension\Core\Type\CollectionType;
use Symfony\Component\Form\FormBuilderInterface;

class UserType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            // ...

            ->add('comments', CollectionType::class, [
                'entry_type' => CommentType::class,
                'allow_add' => true,
                'allow_delete' => true,
                'by_reference' => false,
            ])
        ;
    }

    // ...
}

// src/Controller/UserController.php

use App\Entity\User;
use App\Form\UserType;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\Routing\Annotation\Route;

class UserController extends AbstractController
{
    /**
     * @Route("/user/new", name="user_new", methods={"GET", "POST"})
     */
    public function new(Request $request): Response
    {
        $user = new User();
        $form = $this->createForm(UserType::class, $user);
        $form->handleRequest($request);

        if ($form->isSubmitted() && $form->isValid()) {
            // 保存用户和关联的评论到数据库中
            $entityManager = $this->getDoctrine()->getManager();
            $entityManager->persist($user);
            $entityManager->flush();

            return $this->redirectToRoute('user_show', ['id' => $user->getId()]);
        }

        return $this->render('user/new.html.twig', [
            'form' => $form->createView(),
        ]);
    }

    // ...
}