If you're using the Firebase Admin SDK with Node.js, Firestore always returns the default Firestore database associated with the project. Even if you try to change the URL or initialize a second app with a different name, the Admin SDK currently only lets you access the default Firestore database.

Below is an example of the standard initialization:

JAVASCRIPTCopied
const admin = require("firebase-admin");
const serviceAccount = require("./path/to/serviceAccountKey.json");

admin.initializeApp({
  credential: admin.credential.cert(serviceAccount),
  // Specifying a databaseURL here affects the Realtime Database, not Firestore.
  databaseURL: "https://<APP_ID>.firebaseio.com"
});

// This returns the default Firestore database for your project.
const db = admin.firestore();

Even if you initialize a second app with a custom name:

JAVASCRIPTCopied
const otherApp = admin.initializeApp({
  credential: admin.credential.cert(serviceAccount),
  databaseURL: "https://<APP_ID>.firebaseio.com"
}, 'other');

// This still gives you the default Firestore database.
const defaultFirestore = admin.firestore();
const otherFirestore = otherApp.firestore();

Both defaultFirestore and otherFirestore point to the same default Firestore database. The Admin SDK does not provide a mechanism to access a non-default Firestore database (such as a "system" database) from the same Firebase project.

Workarounds:

• Separate Projects: If you really need to work with separate Firestore databases, consider creating separate Firebase projects. Then you can initialize each project independently (each with its own Firestore instance).

• Feature Request: If multiple Firestore databases support in a single project is critical for your workflow, keep an eye on the official Firebase release notes or consider filing a feature request since this is a known limitation.

For now, the only supported behavior with the Firebase Admin SDK is to work with the default Firestore database tied to your Firebase project.