使用负时间戳按降序对 Firebase 数据进行排序 [英] Sort firebase data in descending order using negative timestamp

问题描述

上面是我的 firebase 数据库的屏幕截图.我正在尝试使用负时间戳按降序对 firebase 数据进行排序.我正在使用以下命令:

above is a screenshot of my firebase database. i am trying to sort firebase data in descending order using negative timestamp. I 'm using the following command:

  const feedRef = database.ref('ducks')
  feedRef.orderByChild('timestamp').on('value', (snapshot, error) => {
    const feed = snapshot.val()})

我一直以与数据库相同的顺序获取提要，而不是像我想要的那样按降序排列.我认为它不起作用，因为鸭子端点没有子名称时间戳我将如何实现这一目标?推送生成的密钥是否有时间戳数据?

i keep getting the feed in the same order as the database not in the descending order like i want.I think its not working because ducks endpoint doesnt have a child name timestamp how would i achieve this? Do the push generated keys have timestamp data ?

推荐答案

当您对快照调用 .val() 时，它会被转换为 JSON 对象.JavaScript 对象中的键根据定义是无序的(尽管许多实现会按字典顺序迭代键).

When you call .val() on a snapshot, it gets converted into a JSON object. And the keys in a JavaScript object are by definition unordered (although many implementations will iterate the keys in lexicographical order).

如果您在 Firebase 数据库上运行查询，则必须确保在按正确顺序获取项目之前未将其转换为 JSON.在您的情况下，通过使用 DataSnapshot.forEach():

If you run a query on the Firebase Database, you must ensure you don't convert it to JSON before you get the items in the right order. In your case, by using DataSnapshot.forEach():

const feedRef = database.ref('ducks')
var feed = [];
feedRef.orderByChild('timestamp').on('value', (snapshot, error) => {
    snapshot.forEach((duckSnap) => {
        const duck = duckSnap.val()
        console.log(duckSnap.key+'='+duck.name);
        feed.push(duck);
    });
});
console.log(feed);

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