prepare_collection

    private function prepare_collection(&$coleccion, $text, $id=0) {
        $idproperty = strtolower(get_class($coleccion[0])) . "_id";
        foreach($coleccion as &$obj) {
            $obj->value = $obj->$idproperty;
            $obj->text = $obj->$text;
            $obj->extras = ($obj->value == $id) ? ' selected' : '';
        }
    }