Firebase观察类型.childAdded每次检索我的所有信息。请协助 [英] Firebase observe with type .childAdded retrieves all my information every time. Please assist

问题描述

根据Firebase文档：

每个现有的孩子触发一次ChildAdded，然后每次将新的孩子添加到指定的路径

所以，我有一个应用程序，顶部有一个小横幅，每当用户得到一个新的信息。您可能已经猜到了，这些消息存储在Firebase中的用户对象的子项中。所以，这是问题，当我加载应用程序，它弹出每个用户的消息。只有在添加新的孩子时才可以调用这个观察事件吗？我不希望每个现有的孩子都被触发，只有当新的孩子被添加。我不希望在核心数据中存储消息引用，并检查每个孩子是否已经存在于核心数据中：/ $ / $>

解决方案

使用

• /docs/reference/ios/firebasedatabase/interface_f_i_r_database_reference.html#a88c088c33be888a2e1ffe1714525307arel =nofollow noreferrer> ref.queryLimitedToLast（1） 。请参阅 Firebase，只接收新生儿。


• 跟踪您本地存储中最新的密钥，然后使用 queryOrderByKey（） .queryStartingAtValue（latestKey）


• 为项目添加时间戳，然后添加 .queryStartingAt（now）对于时间戳> =现在的项目。请参阅如何放弃Firebase数据库中的初始数据

According to Firebase docs:

ChildAdded is triggered once for each existing child and then again every time a new child is added to the specified path

So, I have an app, that has a little banner at the top that pops up every time a user gets a new message. As you could have guessed, these messages are stored in a child in the user object in Firebase. So, here's the problem, when I load the app, it pops up for EVERY message the user has. Is it possible to have this observe event ONLY be called when a new child is added? I don't want it to be triggered for every single existing child, only when a new one is added. I would hate to have to store message references in core data, and do a check for every child to see if it already exists in core data :/

解决方案

A few ways to do this:

• Use ref.queryLimitedToLast(1) when you start. See Firebase, only get new children.
• keep track of the most recent key you've got in your local storage and then query with queryOrderByKey().queryStartingAtValue(latestKey)
• Add a timestamp to the items and then queryOrderByChild("timestamp").queryStartingAt(now) for items with timestamp >= now. See how to discard initial data in a Firebase DB

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