How to add validators on the fly in Symfony2? - forms

Question

I've a password form field (not mapped to User password) to be used in a change password form, along with two other (mapped) fields, first and last.
I've to add validators on the fly: if value for password is blank then no validation should occur. Otherwise a new MinLength and MaxLength validators should be added.
Here is what i've done so far: create the repeated password field, add a CallbackValidator and return if $form->getData() is null.
Then, how can i add validators for minimum and maximum length to $field?
$builder = $this->createFormBuilder($user);
$field = $builder->create('new_password', 'repeated', array(
'type' => 'password',
'first_name' => 'Password',
'second_name' => 'Confirm password',
'required' => false,
'property_path' => false // Not mapped to the entity password
));
// Add a callback validator the the password field
$field->addValidator(new Form\CallbackValidator(function($form) {
$data = $form->getData();
if(is_null($data)) return; // Field is blank
// Here password is provided and match confirm, check min = 3 max = 10
}));
// Add fields to the form
$form = $builder
->add('first', 'text', array('required' => false)) // Mapped
->add('last', 'text', array('required' => false)) // Mapped
->add($field) // Not mapped
->getForm();

Answer 1

Oh well, found a solution myself after a few experiments.
I'm going to leave this question unanswered for a couple of days as one can post a better solution, that would be really really welcome :)
In particular, i found the new FormError part redundat, don't know if there is a better way to add the error to the form. And honestly, don't know why new Form\CallbackValidator works while new CallbackValidator won't.
So, don't forget to add use statements like these:
use Symfony\Component\Form as Form, // Mendatory
Symfony\Component\Form\FormInterface,
Symfony\Component\Validator\Constraints\MinLength,
Symfony\Component\Validator\Constraints\MinLengthValidator;
And the callback is:
$validation = function(FormInterface $form) {
// If $data is null then the field was blank, do nothing more
if(is_null($data = $form->getData())) return;
// Create a new MinLengthValidator
$validator = new MinLengthValidator();
// If $data is invalid against the MinLength constraint add the error
if(!$validator->isValid($data, new MinLength(array('limit' => 3)))) :
$template = $validator->getMessageTemplate(); // Default error msg
$parameters = $validator->getMessageParameters(); // Default parameters
// Add the error to the form (to the field "password")
$form->addError(new Form\FormError($template, $parameters));
endif;
};
Well, and this is the part i can't understand (why i'm forced to prefix with Form), but it's fine:
$builder->get('password')->addValidator(new Form\CallbackValidator($validation));

Answer 2

addValidator was deprecated and completly removed since Symfony 2.3.
You can do that by listening to the POST_SUBMIT event
$builder->addEventListener(FormEvents::POST_SUBMIT, function ($event) {
$data = $event->getData();
$form = $event->getForm();
if (null === $data) {
return;
}
if ("Your logic here") {
$form->get('new_password')->addError(new FormError());
}
});