Adding dynamic elements to Symfony form on PRE_SUBMIT - php

Question

I am trying to use Symfony Form Component with Silex framework at the moment. I added some fields in buildForm method of my form type class. Also user can click on a button and add unlimited textarea element using javascript on the frontend. Now on PRE_SUBMIT event, I do the following to add these fields to the form
$data = $event->getData();
$form = $event->getForm();
foreach ($data as $key => $value) {
if (stristr($key, '_tb_') !== false) {
$id = str_ireplace('_tb_', '', $key);
$form->add('_tb_' . $id, 'hidden');
$form->add('_title_' . $id, 'text', [
'required' => false,
'label' => 'Title',
'constraints' => [
new Length(['min' => 6]),
]
]);
$form->add('_img_url_' . $id, 'text', [
'required' => false,
'label' => 'Image Url',
'constraints' => [
new Url(),
]
]);
$form->add('_img_alt_' . $id, 'text', [
'required' => false,
'label' => 'Image Alt',
'constraints' => []
]);
$form->add('_content_' . $id, 'textarea', [
'required' => true,
'attr' => [
'data-role' => '_richeditor'
],
'constraints' => [
new Length(['min' => 100]),
]
]);
}
}
I can see these fields are added to the form and populated once the form is submitted for the first time but for some reason all the constraints are ignored only for these new added fields. Is there a way to force Form to honour the constraints for the newly added elements?

Answer 1

The form component and validation can be tricky. A easy misconception is that the form type option "required" will imply a NotBlank validation constraint. This is not the case, the docs explain that option to be "superficial and independent from validation" only concerned with form element rendering (HTML5 required attr, label, etc).
To make things trickier, that you are specifying a minimum length constraint, one might assume that no (or zero) length would be considered invalid. This is also not the case. The length validator is only concerned with non-null / non-empty values. :-/
So! Modifying the text area field to include NotBlank() should do the trick:
$form->add('_content_' . $id, 'textarea', [
'required' => true,
'attr' => [
'data-role' => '_richeditor'
],
'constraints' => [
new NotBlank(),
new Length(['min' => 100]),
]
]);