symfony ajax form dynamically modify

Question

I have the following form that contains data from the database it still WIP ( i'm missing a few fields that i didn't add yet). The form loads data in the first select and based on that select i use ajax to populate a second select with options based on the first select ( basically the associations to the selected value). And from there again another select with certain options and so on and at the end when i submit the form i want to generate a report from database based on the data. For the moment i'm stuck with the second field because i always get an error:

This value is not valid.

The form class:

/**
 * @param FormBuilderInterface $builder
 * @param array $options
 */
public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder
        ->add('survey', EntityType::class, [
            'class' => SurveyManager::class,
            'placeholder' => 'Choose option',
            'attr' => [
                'class' => 'field-change',
            ],
        ])
        ->add('headquarter', ChoiceType::class, [
            'choices' => [],
        ])
        ->add('submit', SubmitType::class, [
            'label' => 'Save',
        ])
    ;
}

I'm not reall sure how to fix the error or how should i handle this type of form. Can you help me out guys ?

Based on the answer i did this

$builder->addEventListener(
    FormEvents::PRE_SUBMIT,
    function (FormEvent $event) {
        $form = $event->getForm();

        $data = $event->getData();

        $form->add('headquarter', EntityType::class, [
            'class' => HeadQuarterManager::class,
            'query_builder' => function(HeadQuarterManagerRepository $er) {

                return $er->getHeadquarter($data['survey']);
            },
        ]);
    }
);

But i'm getting this error:

Notice: Undefined variable: data 

Not really sure how to pass the data to the getHeadquarter method so i can return an array of id => name for the select.

Answer 1

When you run the function $form->isValid() , it checks against the form it built in the buildForm function. Any extra fields/value that aren't there will cause this error.

You can change this behaviour by using form events .

Answer 2

In the end this is how i did it:

/**
 * @param FormBuilderInterface $builder
 * @param array $options
 */
public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder
        ->add('survey', EntityType::class, [
            'class' => SurveyManager::class,
            'attr' => [
                'class' => 'field-change',
            ],
        ])
        ->add('submit', SubmitType::class, [

        ])
        ->addEventListener(
            FormEvents::PRE_SUBMIT,
            function (FormEvent $event) {
                $form = $event->getForm();

                $data = $event->getData();
                $modifier = $data['survey'];
                $form->add('headquarter', EntityType::class, [
                    'class' => HeadQuarterManager::class,
                    'query_builder' => function (HeadQuarterManagerRepository $er) use ($modifier) {
                        return $er->getHeadquarter($modifier);
                    },
                ]);
            }
        );
}