Can anyone please tell me why the following isn't working?

h:selectOneMenu value="#{modelosController.selected.idMarca}">
f:selectItems value="#{marcasController.itemsAvailableSelectOne}" />
/h:selectOneMenu>
h:commandButton action="#{modelosController.createByMarcas}" value="Buscar" />

public String createByMarcas() {
          current = new Modelos(selectedItemIndex, current.getIdMarca());
          items =(DataModel)ejbFacade.findByMarcas();
          getPagination().getItemsCount();
          recreateModel();
          return "List";
}

public List<Modelos> findByMarcas(){
    CriteriaQuery cq = (CriteriaQuery) em.createNamedQuery("SELECT m FROM Modelos WHERE m.id_marca :id_marca");
    cq.select(cq.from(Modelos.class));
    return em.createQuery(cq).getResultList();
}

Thank you very much!