Question

在我的离子应用程序中，我正在使用Firebase检索所有已注册的驱动程序及其数据。我的架构如下：

ehara
    Driver
        fjk59KJjkfkjflhghk
            driverId: 1
            location
                 0: 9.086333699999999
                 1: 7.459455999999999

我的问题是这个；如果我仅知道他的driverId，如何查询数据库以获取他的位置？

Answer 1

您将必须执行查询以查找具有给定ID的驱动程序：

//Pass the position of the item on the listview/playlist from previous activity /fragment.
    Intent _intent = getIntent();
    position = _intent.getIntExtra("postion_id", 0);

    player = ExoPlayerFactory.newSimpleInstance(this, new DefaultTrackSelector());

    playerView.setPlayer(player);

    DefaultDataSourceFactory dataSourceFactory = new DefaultDataSourceFactory (this, Util.getUserAgent(this, "exo-demo"));

    ConcatenatingMediaSource concatenatingMediaSource = new ConcatenatingMediaSource();

    //Ensure to populate the allFiles array.

    for (int i = 0; i < allFiles.size(); i++) {

        File currentFile = new File(allFiles.get(i));

        MediaSource mediaSource = new ExtractorMediaSource.Factory(dataSourceFactory).createMediaSource(Uri.parse("file://" + currentFile.getAbsolutePath()));
        concatenatingMediaSource.addMediaSource(mediaSource);

    }
    player.prepare(concatenatingMediaSource);
    //Play from the item selected on the playlist from previous activity/fragment
    player.seekTo(position, C.TIME_UNSET);
    player.setPlayWhenReady(true);


    player.addListener(new Player.EventListener() {
        @Override
        public void onTimelineChanged(Timeline timeline, Object manifest, int reason) {



        }

        @Override
        public void onTracksChanged(TrackGroupArray trackGroups, TrackSelectionArray trackSelections) {

        }

        @Override
        public void onLoadingChanged(boolean isLoading) {

        }

        @Override
        public void onPlayerStateChanged(boolean playWhenReady, int playbackState) {

        }

        @Override
        public void onRepeatModeChanged(int repeatMode) {

        }

        @Override
        public void onShuffleModeEnabledChanged(boolean shuffleModeEnabled) {

        }

        @Override
        public void onPlayerError(ExoPlaybackException error) {

        }

        @Override
        public void onPositionDiscontinuity(int reason) {
            //THIS METHOD GETS CALLED FOR EVERY NEW SOURCE THAT IS PLAYED
            int latestWindowIndex = player.getCurrentWindowIndex();
            if (latestWindowIndex != position) {
                // item selected in playlist has changed, handle here
                position = latestWindowIndex;
                // ...
            }




        }

        @Override
        public void onPlaybackParametersChanged(PlaybackParameters playbackParameters) {

        }

        @Override
        public void onSeekProcessed() {

        }
    });

查询可以匹配多个子节点，因此代码需要在可能的多个结果上使用firebase.database().ref('Driver') .orderByChid('driverId') .equalTo('1') .once('value') .then(function(snapshot) { snapshot.forEach(function(driverSnapshot) { console.log(driverSnapshot.val()); }); })。

由于听起来您的情况下ID已经是唯一的，请考虑使用该ID作为snapshot.forEach节点中的密钥。

Driver

在这种情况下，读取将变成简单的查找（而不是查询）：

Driver
    id1
        location
             0: 9.086333699999999
             1: 7.459455999999999

由于在此结构中只有一个具有给定密钥的节点，因此我们也不再需要firebase.database().ref('Driver') .child('id1') .once('value') .then(function(snapshot) { console.log(snapshot.val()); })循环。

Firebase从实时数据库检索数据

1 个答案: