Symfony 5 add field to form after form submit

Question

Lets assume I have the following form:

public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder
        ->add('paste', TextareaType::class, [
            'attr' => array('rows' => '15'),
        ])
        ->add('language', ChoiceType::class, ['choices' => $this->languagesService->getSupportedLanguages()])
        ->add('visibility', ChoiceType::class, ['choices' => $this->visibilityService->getVisibilities()])
        ->add('expiresAt', ChoiceType::class, ['choices' => $this->expiryService->getExpiryTimes(), 'mapped' => false])
        ->add('name', TextType::class, ['required' => false])
        ->add('save', SubmitType::class, ['label' => 'Submit'])
    ;
}

Once the form is submitted I want to add another field to it that the user cannot complete. Lets call the field in question new_field .

So far I've tried using a form event:

public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder
        ->add('paste', TextareaType::class, [
            'attr' => array('rows' => '15'),
        ])
        ->add('language', ChoiceType::class, ['choices' => $this->languagesService->getSupportedLanguages()])
        ->add('visibility', ChoiceType::class, ['choices' => $this->visibilityService->getVisibilities()])
        ->add('expiresAt', ChoiceType::class, ['choices' => $this->expiryService->getExpiryTimes(), 'mapped' => false])
        ->add('name', TextType::class, ['required' => false])
        ->add('save', SubmitType::class, ['label' => 'Submit'])
        ->addEventListener(FormEvents::POST_SUBMIT, function (FormEvent $event) {
            $form = $event->getForm();
            $form->add('new_field')->setData('some_data');
        })
    ;
}

And I obviously get an exception thrown my way: You cannot add children to a submitted form , which is fair enough.

Another thing I could do, which I very much don't want to do because it seems hacky is create a new entity in the controller, set the data I get from the form there and save it.

if ($form->isSubmitted() && $form->isValid()) {
    $formData = $form->getData();
    $entity = new Paste();
    $entity->setCreatedAt($formData->get('createdAt')->getData());
    ...

I could also create some generic parent to the form and modify that, but that seems even more hacky.

---

I'm not opposed to another approach here. Perhaps I'm looking at this wrong to begin with.

Answer 1

If you want to modify data, you should never call $form->setData() as this is handled internally.

->addEventListener(FormEvents::POST_SUBMIT, function (FormEvent $event) {
    $class= $event->getData();
    $class['new_field'] = 'some_data';
    $event->setData($class);
});

But you can use $event->setData() instead.