How to handle unchecked checkbox in form validation and model binding

[wurst-hans]

Imagine I have a database model

<?php
class Person extends Model {
    public $is_friendly;
}

where the flag is_friendly is an INT column in table and 1 means yes and 0 means no.

Now, I have a form

<?php
class PersonForm extends Form {
    public function initialize() {
        $this->add(new Check('is_friendly', ['value' => 1]));
    }
}

The controller does the following

<?php
class PersonController extends Controller {
    public function updateAction() {
        $entity = Person::findFirst();
        $form = new PersonForm($entity);
        if ($form->isValid($_POST)) {
            $entity->save();
        }
    }
}

When checking the checkbox in HTML form, the value 1 is saved correctly in database. But what does not work, is saving the form with unchecked checkbox.
This is because an unchecked input element is not contained in $_POST payload. Currently, I'm not able to unset a flag, that has been has been set sometime before. I hoped, that I can use beforeValidation() of form class to modify $data, but $data can't be passed by reference to this method. Therefor, I can't modify the previously bound data.
Is the form class of Phalcon able to handle this anyhow? What can a clean solution look like?

[wurst-hans]

Here is a post in old Phalcon forum, but the solution there is not really satisfactory.

Ok, I see, it's an unsolved issue for a long time now, #2890