I'm using the Firebase Admin SDK with Node.js. My Firebase app has some Firestore databases. For example:

• (default)
• system.

But every time I save data, it always goes to the (default) database and I need to change it to the other database. I searched the Firebase documentation, but couldn't find anything.

What I tried:

• Changing via the databaseURL:

admin.initializeApp({
    credential: admin.credential.cert(serviceAccount),
    databaseURL: 'https://<DATABASE_NAME>.firebaseio.com',
})

• Pass a second parameter to the initializeApp function with the name of the DB:

admin.initializeApp({
    credential: admin.credential.cert(serviceAccount),
    databaseURL: 'https://<APP_ID>.firebaseio.com',
}, '<DATABASE_NAME>') // this change the app, no the database 🤦‍♂️

Change the databaseId in the firestore settings.

I found the solution after inspecting firebase-admin's TypeScript types. I don't know if the Firebase documentation mentions this, but I didn't find it there. The solution is simple:

Change the Firestore database by setting the databaseId in the object passed to firestore().settings().

Here's an example to help you understand:

const admin = require('firebase-admin')
const serviceAccount = require('./serviceAccountKey.json')

admin.initializeApp({
    credential: admin.credential.cert(serviceAccount),
    databaseURL: 'https://<YOUR_APP_ID>.firebaseio.com',
})

admin.firestore().settings({
    ignoreUndefinedProperties: true,
    databaseId: 'system', // Here you change your DB
})

const db = admin.firestore()