从 Node.js 中的 Firebase 实时数据库中选择特定属性

Question

Is there any way to select specific properties from firebase Realtime Database? I know there is a way to retrieve selected properties from firestore but how can get via Realtime database using Node.js

I want only Notes from everyone nothing else.

Suppose i just want to select Notes from Allergy here is my sample code which i tried but not successes...

admin.database().ref(`vitals/Allergy`).select('Notes').then(result => {//here is my result.....})

But it shows me that select is not a function.......

Answer 1

Realtime Database doesn't support "projections" like this (neither does Cloud Firestore). If you are going to query across multiple child nodes, you are going to get each entire child node that matches the query. Even if you want just one property of each child, you can't avoid the cost of downloading the entire child.

If your app is very sensitive to performance on these types of queries, consider duplicating the data such that there is another branch of your database that contains only the "Notes" property, and query that branch alone. This duplication is common in NoSQL type databases, and is call the "fan out" technique .

Answer 2

If you want to save download band then i can't help you further, otherelse:

let ArrayOfAllDownloadedNotes = [];
firebase.database().ref('yourRootFolders/vitals/Allergy').once((snapshot)=>{
  ArrayOfAllDownloadedNotes = [...ArrayOfAllDownloadedNotes, snapshot.val().Notes];
});

//Reapeat the firebase formula for every child you want retrieve the Notes from
//You may also use forEach((item)=>{}) function for each folder you want to retrieve the //notes from if you want

console.log(My Array of Notes:',ArrayOfAllDownloadedNotes );