删除2小时以前的Firebase数据 [英] Delete firebase data older than 2 hours

问题描述

我想删除任何两个小时以前的数据。目前，在客户端，我遍历所有的数据，并在任何更旧的版本上运行删除。当我这样做时，db.on（'value'）函数每次被删除时都会被调用。而且，只有在客户端连接时才会删除事件，如果两个客户端连接在一起，会发生什么情况？

我可以在哪里设置删除旧数据的东西？我在JavaScript Date.now（）创建的每个对象中都有一个时间戳记。 Firebase不支持使用动态参数进行查询，例如两小时前。然而， 可以针对特定值执行查询，例如2015年8月14日上午7:27:32之后。

意味着您可以定期运行代码片段来清理当前时间超过2小时的项目 ：

  var ref = firebase.database（）。ref（'/ path / to / items /'）; 
 var now = Date.now（）; 
 var cutoff = now  -  2 * 60 * 60 * 1000; 
 var old = ref.orderByChild（'timestamp'）。endAt（cutoff）.limitToLast（1）; 
 var listener = old.on（'child_added'，function（snapshot）{
 snapshot.ref.remove（）; 
}）; 
  

正如您将会注意到的那样，我使用 child_added 而不是 value 和I limitToLast（1）。当我删除每个孩子时，Firebase将为新的最后项目触发一个 child_added ，直到截止点之后没有更多项目。

更新：如果您想在Firebase的Cloud Functions中运行此代码：

  exports.deleteOldItems = functions.database.ref（'/ path / to / items / {pushId}'）
 .onWrite（event => {
 var ref = event.data.ref （）; 
 var cutoff = now  -  2 * 60 * 60 * 1000; 
 var oldItemsQuery = ref.orderByChild（） 'timestamp'）。endAt（cutoff）; 
 return oldItemsQuery.once（'value'，function（snapshot）{
 //创建一个包含所有需要删除的子元素的映射
 var更新= {}; 
 snapshot.forEach（function（child）{
 updates [child.key] = null 
}）; 
 //一次执行所有更新返回结果来结束函数
 return ref.update（updates）; 
}）; 
}）; 
  

只要数据写在 / path / to / items ，所以子节点只会在数据被修改时被删除。

I would like to delete any data that is older that two hours. Currently, on the client side, I loop through all the data, and run a delete on any that is older. When I do this, the db.on('value') function is invoked every time something is deleted. Also, things will only be deleted when a client connects, and what might happen if two clients connect at once?

Where can I set up something that deletes old data? I have a time stamp inside each object created by a JavaScript Date.now().

解决方案

Firebase does not support queries with a dynamic parameter, such as "two hours ago". It can however execute a query for a specific value, such as "after August 14 2015, 7:27:32 AM".

That means that you can run a snippet of code periodically to clean up items that are older than 2 hours at that time:

var ref = firebase.database().ref('/path/to/items/');
var now = Date.now();
var cutoff = now - 2 * 60 * 60 * 1000;
var old = ref.orderByChild('timestamp').endAt(cutoff).limitToLast(1);
var listener = old.on('child_added', function(snapshot) {
    snapshot.ref.remove();
});

As you'll note I use child_added instead of value, and I limitToLast(1). As I delete each child, Firebase will fire a child_added for the new "last" item until there are no more items after the cutoff point.

Update: if you want to run this code in Cloud Functions for Firebase:

exports.deleteOldItems = functions.database.ref('/path/to/items/{pushId}')
.onWrite(event => {
  var ref = event.data.ref.parent; // reference to the items
  var now = Date.now();
  var cutoff = now - 2 * 60 * 60 * 1000;
  var oldItemsQuery = ref.orderByChild('timestamp').endAt(cutoff);
  return oldItemsQuery.once('value', function(snapshot) {
    // create a map with all children that need to be removed
    var updates = {};
    snapshot.forEach(function(child) {
      updates[child.key] = null
    });
    // execute all updates in one go and return the result to end the function
    return ref.update(updates);
  });
});

This function triggers whenever data is written under /path/to/items, so child nodes will only be deleted when data is being modified.

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