Firebase child_ added 仅适用于新项目 [英] Firebase child_added for new items only

问题描述

我在 Redux 中使用 Firebase 和 Node.我正在从一个键加载所有对象，如下所示.

I am using Firebase and Node with Redux. I am loading all objects from a key as follows.

firebaseDb.child('invites').on('child_added', snapshot => {
})

这种方法背后的想法是，我们从数据库中获取一个有效负载，并且只使用一个操作来通过 Reducers 更新我的本地数据存储.

The idea behind this method is that we get a payload from the database and only use one action to updated my local data stores via the Reducers.

接下来，我需要监听关键邀请的任何NEW 或UPDATED 子级.然而，现在的问题是 child_ added 事件会为所有现有的键以及新添加的键触发.我不想要这种行为，我只需要新密钥，因为我检索了现有数据.

Next, I need to listen for any NEW or UPDATED children of the key invite. The problem now, however, is that the child_added event triggers for all existing keys, as well as newly added ones. I do not want this behaviour, I only require new keys, as I have the existing data retrieved.

我知道 child_ added 通常用于这种类型的操作，但是，我希望减少触发的操作数量，并因此触发渲染.

I am aware that child_added is typically used for this type of operation, however, i wish to reduce the number of actions fired, and renders triggered as a result.

实现这一目标的最佳模式是什么?

What would be the best pattern to achieve this goal?

谢谢，

推荐答案

我已经用下面的方法解决了这个问题.

I have solved the problem using the following method.

firebaseDb.child('invites').limitToLast(1).on('child_added', cb)
firebaseDb.child('invites').on('child_changed', cb)

limitToLast(1) 获取邀请的最后一个子对象，然后侦听任何新的子对象，将快照对象传递给 cb 回调.

limitToLast(1) gets the last child object of invites, and then listens for any new ones, passing a snapshot object to the cb callback.

child_changed 侦听对邀请的任何子更新，将快照传递给 cb

child_changed listens for any child update to invites, passing a snapshot to the cb

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