删除超过 2 小时的 Firebase 数据 [英] Delete firebase data older than 2 hours

问题描述

我想删除超过两个小时的数据.目前，在客户端，我遍历所有数据并对过时的数据运行删除.当我这样做时，每次删除某些内容时都会调用 db.on('value') 函数.另外，只有当一个客户端连接时才会删除东西，如果两个客户端同时连接会发生什么?

I would like to delete data that is older than two hours. Currently, on the client-side, I loop through all the data and run a delete on the outdated data. 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?

在哪里可以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.

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

推荐答案

Firebase 不支持带有动态参数的查询，例如两小时前".但是，它可以对特定值执行查询，例如after August 14 2015, 7:27:32 AM".

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".

这意味着您可以定期运行一段代码来清理当时超过 2 小时的项目:

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();
});

您会注意到，我使用 child_ added 而不是 value，并且我使用 limitToLast(1).当我删除每个子项时，Firebase 会为新的最后一个"项触发 child_ added，直到截止点之后没有更多项.

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.

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

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

exports.deleteOldItems = functions.database.ref('/path/to/items/{pushId}')
.onWrite((change, context) => {
  var ref = change.after.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);
  });
});

每当在/path/to/items下写入数据时都会触发此函数，因此只有在修改数据时才会删除子节点.

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

此代码现在也可在 functions-samples repo.

This code is now also available in the functions-samples repo.

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