Silex / Symfony2 Post-Validation - forms

Question

Im sure this must be a RTM question, but I must be looking in the wrong places. In symfony 1.4 I used post validator callbacks quite a lot. For example checking that start and end dates were in the correct order. I am developing an app in Silex but cant figure out how to add similar functionality as a validator. This is what I am working with (basically):
$app['form.example'] = function ($app) {
$constraints = new Assert\Collection(array(
'date1' => new Assert\Date(),
'date2' => new Assert\Date(),
));
$builder = $app['form.factory']->createNamedBuilder('form', 'example', array(), array('validation_constraint' => $constraints));
return $builder
->add('date1', 'date')
->add('date2', 'date')
->getForm();
};
I can put my own validation test in the 'process form' part, like: if ($form->isValid() && --my datetest--) but it doesnt feel right to me there.
Any help? Thanks!

Answer 1

I guess you can use form events for this kind of thing; certainly for Symfony2, so I assume Silex too? There's a cookbook article about using it to generate dynamic forms:
http://symfony.com/doc/current/cookbook/form/dynamic_form_generation.html
Some useful detail in another SO question:
Description of Symfony2 form events?
Could have sworn I had a SO discussion about this with someone before but I cannot find the question. I used BIND_CLIENT_DATA to calculate some form fields in some code a while back; I'll see if I can dig it out.
EDIT
Okay, I found something but I'm modifying this from Symfony code so I'm not 100% on this but it might be a starting point (I hope):
$builder->addEventListener(FormEvents::BIND_NORM_DATA, function($event) {
// your form data
$data = $event->getData();
// get date objects - if you cannot dereference this way try getters
$d1 = $data['date1'];
$d2 = $data['date2'];
// naive comparison :)
$isCorrectDateOrder = $d1->getTimestamp() < $d2->getTimestamp();
// check the comparison
if (!$isCorrectDateOrder) {
// trouble... create and add a FormError object to the form
$event->getForm()->get('date1')->addError(new \Symfony\Component\Form\FormError('uh oh...'));
}
});
Hope this helps :)