如何使用 Angular 在 Firebase 中仅获取选定的数据列表

Question

Suppose I have two branch in Firebase (eg :- Branch A and Branch B).

Branch A :
 branchA1 :
   field1 : "Hello"
   field2 : "Hello"
branchA2 :
   field1 : "Hello"
   feild2 : "Hello"
branchA3 :
   field1 : "Hello"
   field2 : "Hello"
branchA4 :
   field1 : "Hello"
   field2 : "Hello"
branchA5 :
   field1 : "Hello"
   field2 : "Hello" 



Branch B :
 branchB1 :
   randomID1:
     Id : branchA5
   randomID2:
     Id : branchA1
   randomID3:
     Id : branchA2
 branchB2 :
   randomID1:
     Id : branchA3
   randomID2:
     Id : branchA4

So suppose user selected id is branchB2 then how can I select only branchA3 and branchA4 from branchA using Angular JS?

Answer 1

Divide this procedure in 2 steps then it should be pretty straightforward.

1. Get branchB2 and read IDs of it's child nodes
2. Make another request to get those nodes from branch A.

// Getting branch B2
const dbRef_B = firebase.database().ref("branchB/branchB2")
const dbVal = (await dbRef_B.once("value")).val()

// Reading child nodes
const branchA_Keys = Object.values(dbVal).map(b => b.Id)

// Make separate requests for these IDs
const requests = branchA_Keys.map((key) => firebase.database().ref(`branchA/${key}`).once("value"))

// Running all requests simultaneously using Promise.all()
const snapshots = await Promise.all(requests)
const data = snapshots.map(snap => snap.val())

console.log(data)