如果字段为空，则在嵌入式表单中编辑父实体时删除子实体- Symfony 4

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

// ...

$builder->add('children', CollectionType::class, [
    'entry_type' => ChildType::class,
    'allow_add' => true,
    'allow_delete' => true,
    'by_reference' => false,
]);

use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\HttpFoundation\Request;

class ParentController extends AbstractController
{
    // ...

    public function edit(Request $request, ParentEntity $parent)
    {
        // 创建表单并与父实体绑定
        $form = $this->createForm(ParentType::class, $parent);

        // 处理表单的提交
        $form->handleRequest($request);

        if ($form->isSubmitted() && $form->isValid()) {
            // 保存父实体及其子实体
            $entityManager = $this->getDoctrine()->getManager();
            $entityManager->persist($parent);
            $entityManager->flush();

            // 跳转到成功页面或其他操作
        }

        // 渲染表单视图
        return $this->render('parent/edit.html.twig', [
            'form' => $form->createView(),
        ]);
    }

    // ...
}