DoctrineChoice query

gistfile1.txt

$relatedStrainQuery = Doctrine_Query::create()
            ->select('id')
            ->from('Strain s')
            ->where('s.lab_id = ?', $this->getOption('pref_lab_id'));

$this->widgetSchema['strain_id'] = new sfWidgetFormDoctrineChoice(array(
                                                          'model' => $this->getRelatedModelName('Strain'),
                                                          'query' => $relatedStrainQuery,
                                                          'multiple' => false,
                                                          'add_empty' => true
                                                          ));

//I tried with 'model' => 'Strain' as well, but it makes no difference