我怎样才能将pqxx :: prepare :: invocation中的语句作为std :: string来获取？

Question

示例：

    pqxx::connection c("dbname=mydb user=user");
    pqxx::work w(c);

    c.prepare("Prepared_Statement", "SELECT id  FROM mytable WHERE id = $1 or id = $2");

    pqxx::prepare::invocation w_invocation = w.prepared("Prepared_Statement");

但我无法使用此语句声明游标，它希望查询为std :: string：

    pqxx::stateless_cursor<pqxx::cursor_base::read_only, pqxx::cursor_base::loose> cursor(w, w_invocation , "cname", false);