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

问题描述

：

  const feedRef = database.ref（'ducks'）
 var feed = []; $（$）$ b $ 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）; 
  

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()})

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 ?

解决方案

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).

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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