How to handle multiple Firebase FCM tokens per user?

Question

From the official documentation I understand that the way it works is something like this:

1. User installs app, FCM token is generated
2. Sending token to app server
3. Server uses token to send push-notifications to this device.

What if at the same time this user installs app on the other device - should I store multiple tokens per user on the app server? If yes - that means there should be something like checking for which ones are expired?

Answer 1

I also came across the exact challenge and had to resolve to a solution: Storing each token for the user against the device id. It's interesting enough to know that this function in fact exists in the firebase messaging method. But more surprising is the fact that there's no documentation to handle such scenario. https://firebase.google.com/docs/reference/android/com/google/firebase/iid/FirebaseInstanceId.html#getId()

Summarily, while sending the new token to the server, also send along the device id returned by the getId() method and use it to enforce uniqueness of token per device.

And to also apply this solution while taking advantage of device grouping feature of FCM, you can make a server request on the FCM group, in order to delete the old token on that device-id before replacing it with the new.

Answer 2

What if at the same time this user installs app on the other device - should I store multiple tokens per user on the app server?

Yes. A user could have multiple devices, a case where Device Groups are commonly used.

If yes - that means there should be something like checking for which ones are expired?

If a token expires, a callback is triggered (onTokenRefresh() for Android), from where you'll have to send the new token to your App Server and delete the old one corresponding to the user/device.