Q:

Symfony form builder: How to iterate/render dynamic amount of text fields in twig? (Sylius - exta checkout step)

I added an extra checkout step to the Sylius checkout procedure and I am trying to add 1 text field per instance of an ordered item. Thus having put 3x itemA and 1x itemB in cart should spawn 4 text fields. 
I have this code so far in the form builder (based on code from here: https://sf.khepin.com/2011/08/basic-usage-of-the-symfony2-collectiontype-form-field/)
        $builder->add('myCollection', CollectionType::class, $formOptions);

        $totalCounter = 0;
        /** @var OrderItem $item */
        foreach($order->getItems() as $item) {
            for($itemCounter = 0 ; $itemCounter < $item->getQuantity(); $itemCounter++ ) {
                $totalCounter++;
                $builder->get('myCollection')->add('item_' . $totalCounter, TextType::class, $formOptions);
            }
        }

First Question: Is this the right approach for the form builder for my particular scenario, and secondly: If yes, how do I read from this in the twig template? 
form.children.myCollection does exist but does not seem to contain these children, so that I could use them with the form_row function. What I would have expected is something like this:
{% set totalCounter = 0 %}
{% for item in order.items %}
    {% for itemCounter in 1..item.quantity %}
        {% set totalCounter = totalCounter + 1 %}
        {{  form_row(form.children.myCollection['item_' ~ totalCounter ]) }}
    {% endfor %}
{% endfor %}

Any idea how to do this? Thanks for any hint in advance!

A:

Just saw my exact case is described in the beginning of the documentation of CollectionType https://symfony.com/doc/current/reference/forms/types/collection.html
The form builder part..
$builder->add('emails', CollectionType::class, [
    // each entry in the array will be an "email" field
    'entry_type' => EmailType::class,
    // these options are passed to each "email" type
    'entry_options' => [
        'attr' => ['class' => 'email-box'],
    ],
]);

..and the twig part:
{{ form_label(form.emails) }}
{{ form_errors(form.emails) }}

<ul>
{% for emailField in form.emails %}
    <li>
        {{ form_errors(emailField) }}
        {{ form_widget(emailField) }}
    </li>
{% endfor %}

