Firebase Firestore订单因无法正常工作 [英] Firebase Firestore order by not working

问题描述

我正在通过官方文档了解有关Firebase Firestore的信息.我正在尝试下面的代码.通知是使用firestore的add()方法添加的.

I am learning about Firebase Firestore through official documentation. I was trying following code. Notifications are added using add() method of firestore.

FirebaseFirestore.getInstance().colRefNotifications()
            .orderBy("timestamp", Query.Direction.DESCENDING)
            .get()
            .addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
        @Override
        public void onSuccess(QuerySnapshot documentSnapshots) {

            if (!documentSnapshots.isEmpty()){

                listNotifications.clear();
                recyclerViewNotification.removeAllViews();

                for (DocumentSnapshot data : documentSnapshots){

                    Notification notification = data.toObject(Notification.class);
                    listNotifications.add(notification);
                }

                notificationGeneralAdapter.notifyDataSetChanged();
            }
        }
    });

Notification.java

private String text;
private String key;
private Date timestamp;

public Notification() {
}

public Notification(String text, String key, Date timestamp) {
    this.text = text;
    this.key = key;
    this.timestamp = timestamp;
}

public String getText() {
    return text;
}

public String getKey() {
    return key;
}

public Date getTimestamp() {
    return timestamp;
}

Firestore

我正在按时间戳降序排列通知.但是，如下面的快照所示，它没有显示所需的输出.

I am ordering notifications by timestamp in descending direction. But, as you can see in the following snapshot, it is not showing desired output.

我做错了什么?谢谢您的帮助.

What am I doing wrong? Thank you for your help.

推荐答案

这是由于嵌套查询而发生的.如果将查询放入侦听器中(成功/失败/完成)，orderBy方法将不起作用.将您的下一个查询放入RecyclerView适配器的onBindViewHolder中.

This is happening because of nested queries. If you put a query inside a listener (success/failure/complete), orderBy method will not work. Place your next query inside onBindViewHolder of the RecyclerView adapter.

FirebaseFirestore.getInstance().colRefNotifications()
        .orderBy("timestamp", Query.Direction.DESCENDING)
        .get()
        .addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
    @Override
    public void onSuccess(QuerySnapshot documentSnapshots) {

        if (!documentSnapshots.isEmpty()){
           ....

           /**If you are nesting queries like this, move second query to**/
           /**onBindViewHolder of the RecyclerView adapter**/

           FirebaseFirestore.getInstance().colRefUsers()
           .get()
           .addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
           @Override
           public void onSuccess(QuerySnapshot documentSnapshots) {

               if (!documentSnapshots.isEmpty()){
               ....

               }
             }
          });
        }
    }
});

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