blah.php

<?php

class zdComparatorForm extends sfForm
{
  public function setup()
  {
    $this->setWidgets(array(
      'product_line' => new sfWidgetFormPropelChoice(array('add_empty' => true, 'model' => 'zdProductLine')),
      'model' => new sfWidgetFormChoice(array('choices' => new sfCallable(array($this, 'getModelChoices')))),
    ));

    $this->setValidators(array(
      'product_line' => new sfValidatorPropelChoice(array('model' => 'zdProductLine')),
      'model' => new sfValidatorCallback(array('callback' => array($this, 'validateModel'))),
    ));

    $this->widgetSchema->setNameFormat('zd_comparator[%s]');
  }
}