function delete_values(Resume_Field $field)
    {
        global $wpdb;
        $group_names = $field->get_group_names();
        $field_name = $field->get_name();
        $meta_key_constraint = '`meta_key` LIKE "' . $field_name . implode('-%" OR `meta_key` LIKE "' . $field_name, $group_names) . '-%"';
        return $wpdb->query('
			DELETE FROM ' . $wpdb->usermeta . '
			WHERE (' . $meta_key_constraint . ') AND `user_id`="' . intval($this->user_id) . '"
		');
    }