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 public function configure()
  {
   $this->validatorSchema->setPostValidator(
      new sfValidatorCallback(array('callback' => array($this, 'checkRefund')))
    );

  }
}
  public function checkRefund($validator, $values)
  {
    if ((!empty($values['result_id']) && $values['result_id'] == 3) && $values['cancel_reason'] ==  '')
    {
      $error = new sfValidatorError($validator, 'Vous devez préciser la raison de cette annulation');

      // throw an error bound to the password field
      throw new sfValidatorErrorSchema($validator, array('cancel_reason' => $error));
    }

    return $values;
  }