Android中的Firebase数据描述排序

Firebase Data Desc Sorting in Android(Android中的Firebase数据描述排序)

问题描述

我将数据存储在 Firebase 存储中.

I am storing data in Firebase storage.

对象 Comment 带有属性 timestamp.当我将数据从设备推送到 Firebase 时，我使用 currentTime 填充 timestamp 并存储在 long 数据类型中.

Object Comment with attribute timestamp. When I push data from device to Firebase I'm populating timestamp with currentTime and store in long data type.

当我使用 firebaseRef.orderByChild("timestamp").limitToLast(15) 检索数据时，结果未按预期排序.

When I do retrieving the data with firebaseRef.orderByChild("timestamp").limitToLast(15) result is not sorting how I expected.

我什至玩弄规则却没有结果:

I even played around with rules and no result:

{
    "rules": {
        ".read": true,
        ".write": true,
        ".indexOn": "streetrate",
        "streetrate": {
          ".indexOn": ".value"
        }
    }
}

我尝试将 timestamp 存储在 String 数据类型中，同样的问题.

I tried store timestamp in String data type, same issue.

推荐答案

Firebase 可以按给定属性对项目进行升序排序，然后返回前 N 个项目 (limitToFirst()) 或最后 N 项 (limitToLast()).无法表明您希望项目按降序排列.

Firebase can order the items in ascending order by a given property and then returns either the first N items (limitToFirst()) or the last N items (limitToLast()). There is no way to indicate that you want the items in descending order.

有两个选项可以得到你想要的行为:

There are two options to get the behavior you want:

1. 使用 Firebase 查询获取正确的数据，然后在客户端重新排序

1. Use a Firebase query to get the correct data, then re-order it client-side

向数据中添加一个具有降序值的字段

Add a field that has a descending value to the data

对于后一种方法，通常使用倒置时间戳.

For the latter approach, it is common to have a inverted timestamp.

-1 * new Date().getTime();

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