Flutter Firebase Database wrong timestamp order

问题

I'm trying to set timestamp into firebase realtime database but when I retrieve, not ordering by timestamp. I did like so.

FirebaseDatabase.instance.reference().child('path').push().set({
      'timestamp': ServerValue.timestamp
    });

This is the node

Then I retrieve like so.

FirebaseDatabase.instance.reference().child('path').orderByChild('timestamp').once().then((snap) {
            print(snap.value);
          });

but output is this

{-LJhyfmrWVDD2ZgJdfMR: {timestamp: 1534074731794}, -LJhyWVi6LddGwVye48K: {timestamp: 1534074689667}, -LJhzDlvEMunxBpRmTkI: {timestamp: 1534074875091}

Those are not ordered by timestamp. Am I missing something? Otherwise is this firebase error or flutter?

回答1:

The data is retrieved in the right order into a DataSnapshot. But when you call snap.value the information from the snapshot has to be converted into a Map<String, Object>, which not longer can hold information about the order of the child nodes.

To maintain the order, you have to process the child nodes from the DataSnapshot with a loop. I'm not an expert in Flutter (at all), but I can't quickly find a way to do this for a value event. So you might want to instead listen for .childAdded:

   FirebaseDatabase.instance
        .reference()
        .child('path')
        .orderByChild('timestamp')
        .onChildAdded
        .listen((Event event) {
      print(event.snapshot.value);
    })

来源：https://stackoverflow.com/questions/51808719/flutter-firebase-database-wrong-timestamp-order

标签

firebase-realtime-database

Flutter