{Firebase-javascript} 如何从实时数据库的两条路径中查询数据

Question

I want to query data from two path reference. Here is my database structure

The data that I want are sum_powder from date of 2-3 (reference are "History/Sum/2021/6/2" and "History/Sum/2021/6/3") and included data in one array but I try this code my data is null. What should I do? Thank you for your help.

var path1 = firebase.database().ref().child("History/Sum/2021/6/2")
var path2 = firebase.database().ref().child("History/Sum/2021/6/3")

path1.on('child_added', snap => {
    path2.child(snap.val().timestamp).once('value', data => {
        console.log("join : ",data.val())
    })
})

Answer 1

Try running both the promises in a Promise.all() :

var path1 = firebase.database().ref().child("History/Sum/2021/6/1").once("value")
var path2 = firebase.database().ref().child("History/Sum/2021/6/2").once("value")

Promise.all([path1, path2]).then((response) => {
  const [path1Snap, path2Snap] = response

  //Logging the values
  console.log("Value of path 1", path1Snap.val())
  console.log("Value of path 2", path2Snap.val())
})

The response is an array of snapshots received from Firebase.