public function batch_init() {

        global $wpdb;
        $members = array();

        $query = "
                    SELECT u.ID FROM $wpdb->users u
                    LEFT JOIN $wpdb->pmpro_memberships_users mu ON u.ID = mu.user_id
                    LEFT JOIN $wpdb->pmpro_membership_levels m ON mu.membership_id = m.id
                    WHERE mu.membership_id > 0
                    GROUP BY u.ID
                    ORDER BY u.user_registered ASC
                    ";

        $result = $wpdb->get_results( $query, ARRAY_A );

        if ( ! empty( $result ) ) {
            foreach ( $result as $member ) {
                $members[] = $member['ID'];
            }
        }

        return $members;
    }