database update notification in firebase for specific users

Question

I am trying to create an android application and would like to use firebase database. As I read firebase allows instant messaging and also notify clients when database is updated. I need to create a database and when any database changes happen, related users needs to be notified only. Is that possible with firebase or should I use backend server for this purpose?

Answer 1

You can do it using the Firebase only. What you needs are

1. Firebase Database (Realtime database/Firestore)
2. Firebase Cloud Functions
3. Firebase Cloud Messaging (FCM)

You should write two side codes:

1. Client side (Android)
2. Server side (Cloud Functions)

In Client side (Android)

1. You should register token. (To send a notification using the FCM, Token is needed.) You can do this easily (https://firebase.google.com/docs/cloud-messaging/android/client)

2. I recommend that you can store the token into the database/firestore too. for example:

   class User { long id; String email; String token; }

3. You may write the code to modify the database/firestore.

4. Implement receiving code (https://firebase.google.com/docs/cloud-messaging/android/receive)

In Server side (Cloud Functions)

1. Add some trigger to the database/firestore.
2. Get the token from the database/firestore
3. just send FCM message (https://firebase.google.com/docs/cloud-messaging/admin/send-messages)

You can get the sample code for Server side (Cloud Functions) https://github.com/firebase/functions-samples/tree/master/fcm-notifications

Answer 2

Yes you can achieve this using Firebase Cloud Functions which:

lets you automatically run backend code in response to events triggered by Firebase features and HTTPS requests. Your code is stored in Google's cloud and runs in a managed environment.

And with Firebase Cloud Messaging which:

Is a cross-platform messaging solution that lets you reliably deliver messages at no cost. Using FCM, you can notify a client app that new email or other data is available to sync. You can send notification messages to drive user re-engagement and retention.

So you can write a function in Firebase Cloud Functions which will trigger a notification every time something is changing in your database. Both documetations are very well explained.