Only specific category product show on shop page woocommerce wordpress

add_action('pre_get_posts','shop_filter_cat');

 function shop_filter_cat($query) {
    if (!is_admin() && is_post_type_archive( 'product' ) && $query->is_main_query()) {
       $query->set('tax_query', array(
                    array ('taxonomy' => 'product_cat',
                                       'field' => 'slug',
                                        'terms' => 'ring'
                                 )
                     )
       );  
    }
 }