Firebase:观察childAdded返回现有/旧记录? [英] Firebase: observing childAdded returns existing / old records?

问题描述

我有一个查询(快速编写):

I have a query (written in swift):

    FIRDatabase.database().reference(withPath: "\(ORDERS_PATH)/\(lId)")
      .child("orders")
      .observe(.childAdded, with: { firebaseSnapshot in

      let orderObject = firebaseSnapshot.value as! [String: AnyObject]

      let order = AppState.Order(
        title: orderObject["name"] as! String,
        subtitle: orderObject["item_variation_name"] as! String,
        createdAt: Date(timeIntervalSince1970: TimeInterval(orderObject["created_at"] as! Int / 1000)),
        name: "name",
        status: AppState.Order.Status.Pending
      )

      f(order)
    })

我的数据库如下:

我希望它只监听所有新收到的订单.但是，每次初次加载时，它都会获取一堆现有订单，这不是我想要的.

I want it to just listen all NEW incoming orders. However, every time it initially loads it fetched a bunch of existing orders with it, which isn't what I want.

我在每个订单上确实都有一个created_at(代表该时间的int，例如1478637444000)，因此，如果有可以利用的解决方案也可以使用.

I do have a created_at (an int that represents that time e.g. 1478637444000) on each of the orders, so if there's a solution that can utilize that that works too.

我的查询出问题了吗?

推荐答案

观察者总是触发一次并读入所有数据".

Observers always fire once and read in "all the data".

.value观察者一次读取节点中的所有内容，其中作为.childAdded观察者(来自文档)

A .value observer reads in everything in the node at once, where as a .childAdded observer (from the docs)

为每个现有孩子触发一次此事件，然后再次触发 每次将新子项添加到指定路径时.

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

如果您考虑自己的问题，那么您实际要查找的是所有数据的子集.这是通过查询实现的.

If you think about your question, what you are actually looking for is a sub-set of all of your data. This is achieved via a query.

您的查询将观察在某个时间戳记之后发生的所有.childAdded事件.这就是您需要做的！

Your query will be to observe all .childAdded events that occur after a certain timestamp. So that's what you need to do!

利用queryStartingAtValue(开始的时间戳)创建观察查询，该查询将返回在该时间戳之后添加的所有子项.

Craft an observe query leveraging queryStartingAtValue(the timestamp to start at) which will return all children added after that timestamp.

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