这是一个很好的问题.想到的一种解决方案是制作未映射的表单，并使用表单事件手动绑定数据，例如:

This is a pretty good question. One solution that comes to mind is making an unmapped form and binding data manually using a form event, for example:

public function buildForm(FormBuilderInterface $builder, array $options)
{
    // Make a "nested" address form to resemble JSON structure
    $addressBuilder = $builder->create('address', 'form')
        ->add('place')
        ->add('street');

    $builder->add('username');
    $builder->add('email', 'email');
    $builder->add('password', 'password');
    // add that subform to main form, and make it unmapped
    // this will tell symfony not to bind any data to user object
    $builder->add($addressBuilder, null, ['mapped' => false]);

    // Once form is submitted, get data from address form
    // and set it on user object manually
    $builder->addEventListener(FormEvents::POST_SUBMIT, function (FormEvent $event) {
        $user = $event->getData();
        $addressData = $event->getForm()->get('address')->getData();

        $user->setStreet($addressData['street']);
        $user->setPlace($addressData['place']);
    })
}