protected function addField($name)
 {
     switch ($name) {
         case 'taxonomy':
             $choices = array();
             $choices[null] = null;
             foreach (QubitTaxonomy::getEditableTaxonomies() as $taxonomy) {
                 $choices[$this->context->routing->generate(null, array($taxonomy, 'module' => 'taxonomy'))] = $taxonomy;
             }
             $this->form->setDefault($name, null);
             $this->form->setValidator($name, new sfValidatorString());
             $this->form->setWidget($name, new sfWidgetFormSelect(array('choices' => $choices)));
             break;
     }
 }