Wait for future to complete

Question

I use my postgres database query to determine my next action. And I need to wait for the results before I can execute the next line of code. Now my conn.query returns a Future but I can't manage to get it async when I place my code in another function.

main() {
  // get the database connection string from the settings.ini in the project root folder 
  db = getdb();
  geturl().then((String url) => print(url));
}

Future geturl() {
  connect(db).then((conn) {
    conn.query("select trim(url) from crawler.crawls where content IS NULL").toList()
      .then((result) { return result[0].toString(); })
      .catchError((err) => print('Query error: $err'))
      .whenComplete(() {
        conn.close();
      });
  });
}

I just want geturl() to wait for the returned value but whatever I do; it fires immediately. Can anyone point me a of a piece of the docs that explains what I am missing here?

Answer 1

You're not actually returning a Future in geturl currently. You have to actually return the Futures that you use:

Future geturl() {
  return connect(db).then((conn) {
    return conn.query("select trim(url) from crawler.crawls where content IS NULL").toList()
      .then((result) { return result[0].toString(); })
      .catchError((err) => print('Query error: $err'))
      .whenComplete(() {
        conn.close();
      });
  });
}