protected static String getSorting(Class<?> cls) {
        String r = "";
        for (Field f : cls.getFields()) {
            if (f.isAnnotationPresent(SortBy.class))
                r += (r.length() == 0 ? "" : " ,") + f.getName()
                        + (f.getAnnotation(SortBy.class).reverse() ? " DESC" : " ASC");
        }
        return r;
    }