有没有办法从某个索引获取firebase元素?

编程入门行业动态更新时间:2024-10-28 21:17:26

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我有一个按时间戳排序的聊天消息列表，并且具有唯一的Firebase密钥(由推送操作员创建)

I have a list of chat messages that are ordered by timestamp and have a unique firebase key (made by the push operator)

在此列表中，我想从末尾获得消息，位置为100，但不知道其密钥. 有办法吗?

In this list I want to get the message at position 100 from the end without knowing its key. Is there a way to do this?

我尝试同时使用限制方法limitToLast()和limitToFirst，这创建了一个错误，说明已经设置了过滤器.

I tried using the filtering methods limitToLast() and limitToFirst together which created an error, saying a filter was already set.

我当前的操作方式是使用以下命令下载所有100条消息:

The current way I do it is by downloading all 100 messages with:

admin.database().ref("path/to/messages").limitToLast(100)

然后我在列表中查找我想要的第一把钥匙.

And then I look into that list for the first key which is the one I want.

还有一种方法可以获取第100条消息而不下载其他所有消息吗?

Is ther a way that I can get the 100th message without downloading all the other messages as well?

推荐答案

Firebase Realtime数据库查询不支持指定偏移量，而是要求您知道锚点文档的键值.如果您不了解这些内容，则必须在搜索文档之前/之后阅读所有文档.

Firebase Realtime Database queries don't support specifying an offset, but instead require that you know the key values of the anchor document. If you don't know those, you will have to read all documents before/after the one you search for.