Forms "dynamic" validators

form.html

<form method="post">
    <div>
        <label>First <input type="radio" name="choice" value="1" /></label>
        <input type="text" name="first_text" />
    </div>
    <div>
        <label>Second <input type="radio" name="choice" value="2" /></label>
        <input type="text" name="second_text" />
    </div>
</form>

gistfile1.php

<?php
/**
 * @assert:callback(methods={"isValid"})
 */
class Entity
{
    public $choice;

    /**
     * @var string
     * 
     * @assert:NotBlank(groups="firstGroup")
     */
    private $firstText;

    /**
     * @var string
     * 
     * @assert:NotBlank(groups="secondGroup")
     */
    private $secondText;

    public function isValid(ExecutionContext $context)
    {
        if ($this->radioButton === '1') {
            $context
                ->getGraphWalker()
                ->walkReference($this, 'firstGroup', $context->getPropertyPath().'.firstText', true)
            ;
        } else {
            $context
                ->getGraphWalker()
                ->walkReference($this, 'secondGroup', $context->getPropertyPath().'.secondText', true)
            ;
        }
    }
}