如何在“n”后删除firebase数据天 [英] How to delete firebase data after "n" days

问题描述

我想从我的Friebase中删除一些旧数据。我知道这个问题在这里问了很多，但我仍然很难做到这一点。

我在这里找到这个解决方案：
$ b

Firebase聊天 - 删除旧消息

但这个不推荐使用。

所以我试试这样：

  ChildEventListener childEventListener = new ChildEventListener（）{
 @Override 
 public void onChildAdded（DataSnapshot dataSnapshot，String s）{
 
 Calendar calendar = Calendar.getInstance（）; 
 calendar.add（Calendar.DAY_OF_MONTH，-30）; 
 
 
 Log.d（TAG，onChildAdded：+ dataSnapshot.getKey（））; 
 
 String key = dataSnapshot.getKey（）; 
 
标记retrievemarker = dataSnapshot.getValue（Marker.class）; 
 Calendar t3 = new 
 GregorianCalendar 
（c.get（Calendar.YEAR），
 c.get（Calendar.MONTH），
 retrievemarker.getSavedate（）） ; 
 
 int date1 = calendar.get（Calendar.DATE）; 
 int date2 = t3.get（Calendar.DATE）; 
 
 Log.d（date1，+ date1）; 
 Log.d（date2，+ date2）; 
 
 if（date1 == date2）{
 
 myRef.child（key）.setValue（null）; 
 
 
 
 
 
 $ b $ p 
在我的Firebase中，一个名为Marker的对象，这个对象有一个变量来存储保存的对象在Firebase中保存的日期。
  int date = c.get（Calendar.DATE）; 
 marker.setSavedate（date）; 
  
我想在30天后删除Firebase中的对象。所以我尝试从Date Date减去30天比我想比较这与从Object的savedate，如果它等于我将从Firebase删除对象。
 
 
对于减法我参考以下答案：
 
 
  
 
 
 
但是它dosen'd工作。如果我今天添加一个对象到Firebase，两个日期是相等的。 
所以我想减法不工作。 
 
 
 
我做错了什么？ 
 
解决方案
一个带节点的数据结构如下：
 
 
  -KItqNxLqzQoLnUCb9sJaddclose 
 time：Thu Apr 28 17:12:05 PDT 2016
 timestamp：1461888725444 
  
每个这样的节点都有一个时间戳属性，指明它的创建时间。您最好使用服务器时间戳设置此属性 。
 
 
使用这个数据结构，您可以轻松构建一个只返回超过30天的项目并将其删除的查询： 
 $ b  $ b 
  long cutoff = new Date（）。getTime（） -  TimeUnit.MILLISECONDS.convert（30，TimeUnit.DAYS）; 
 Query oldItems = ttlRef.orderByChild（timestamp）。endAt（cutoff）; 
 oldItems.addListenerForSingleValueEvent（new DataEventListener（）{
 @Override 
 public void onDataChange（DataSnapshot snapshot）{
 for（DataSnapshot itemSnapshot：snapshot.getChildren（））{
 itemSnapshot.getRef（）。removeValue（）; 
} 
} 
 $ b $ @覆盖
 public void onCancelled（DatabaseError databaseError）{
 throw databaseError。 toException（）; 
} 
}）; 
  
 
I want do delete some old data from my Friebase. I knew this question asked a lot here, but i have still a hard time do make it work. 


I try this solution found here:

Firebase chat - removing old messages

but this ist deprecated.

so i try it this way:
ChildEventListener childEventListener = new ChildEventListener() {
    @Override
    public void onChildAdded(DataSnapshot dataSnapshot, String s) {

        Calendar calendar = Calendar.getInstance();
        calendar.add(Calendar.DAY_OF_MONTH, -30);


        Log.d(TAG, "onChildAdded:" + dataSnapshot.getKey());

        String key = dataSnapshot.getKey();

        Marker retrievemarker =dataSnapshot.getValue(Marker.class);
        Calendar t3 = new           
        GregorianCalendar
        (c.get(Calendar.YEAR),
         c.get(Calendar.MONTH),
         retrievemarker.getSavedate());

        int date1= calendar.get(Calendar.DATE);
        int date2= t3.get(Calendar.DATE);

        Log.d("date1",""+date1);
        Log.d("date2",""+date2);

        if( date1 == date2 ){

            myRef.child(key).setValue(null);

        }
for explanation:
In my Firebase i save a object named Marker, this object got a variable to store the savedate, the date where the object was saved in the Firebase.
int date = c.get(Calendar.DATE);
marker.setSavedate(date);
I want to delete the object in the Firebase after 30 days. So i try to subtract 30 days from the Date Today than i want to compare this with the savedate from the Object if it equals i will delete the object from the Firebase.

For the Substraction i refer to the following answer:

How to subtract X days from a date using Java calendar?

But it dosen´t work. If i add a Object today to the Firebase the two dates are allways equal. 
So i guess the subtraction dosen´t work. 

What am I doing wrong?
解决方案
Say that you have a data structure with nodes line this:
-KItqNxLqzQoLnUCb9sJaddclose
  time: "Thu Apr 28 17:12:05 PDT 2016"
  timestamp: 1461888725444
Each such node has a timestamp property that indicates when it was created. Preferably you'd set this property using Server Timestamp.

With this data structure, you can easily build a query that returns only the items older than 30 days and removes them:
long cutoff = new Date().getTime() - TimeUnit.MILLISECONDS.convert(30, TimeUnit.DAYS);
Query oldItems = ttlRef.orderByChild("timestamp").endAt(cutoff);
oldItems.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot snapshot) {
        for (DataSnapshot itemSnapshot: snapshot.getChildren()) {
            itemSnapshot.getRef().removeValue();
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        throw databaseError.toException();
    }
});


                        
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