Develop Reference

Sending push notification to a specific user in cloud function FCM

Please note that this question is not about getting device token on client side.
I am very new to react-native and firebase and I want to implement push notication service of FCM. What I am planning to do is to send a notification to particular device using its device token on my nodejs app server or cloud function( not through console). But as I have found, FCM doesn't provides any API to accrss token by username. Suppose I want to send notification to user X( for the time being, suppose that one user signs only on single device). Now using the function sendToDevice(), I can send the message to a specific device. But how would I know the device token of user X. Do I need to store tokens in the firebase database by myself? Or can I get along without storing FCM tokens?
Please guide me because firebase docs aren't clear about this.

Save the device token for a particular user in DB and then you can use fcm-node npm in which there is a simple function to send a push to a particular device token.
You also need to use the FCM server key which you will get easily on the firebase console.

FCM doesn't offer a way to associate device tokens to individual users who might be using your app from multiple devices. You will need to write code to associate a device token to a user account by sending that token to your backend, along with the user's ID. Only then can you collect FCM tokens for that user, and message them on any of their devices.

FCM Notification to specific wordpress user

i am developping an android application based on a wordpress blog where users can post their own articles, i work with WP REST API to get posts , comments and users ...
I would like to send a notification automatically to the user when his article got a new comment , i have installed FCM correctly and tested the simple forme of notifications but i need to :
Trigger FCM Notification on new comment sent ( Or just on a button click )
Specify receiver so the notification is sent to logged in user with the right email/username
I thought of
working with setting User Property for every user logged like this :
mFirebaseAnalytics.setUserProperty("user_name_for_notification", "the_username");
Sending notification for all devices then handle it in onMessageReceived
but i don't think those are good ideas
So , any ideas where to start
thank you

FCM can send notifications with three different targeting methods:
to a specific FCM token/instance ID token, which identifies an installation of a specific application on a specific device.
to a group of such device/instance IDs.
to a specific topic, which FCM clients can subscribe to.
Firebase Cloud Messaging does not have the concept of a user, therefor it cannot target users directly. If you want to target users, you will have to map them to one of the targeting methods outline above.
The most common ways that I know of:
Store the token(s) for a user in a database under their UID, and then send to the user's token(s) when you need to target the user.
Give each user their own topic, based on their UID. Have the app subscribe to that topic, and send message to the user's topic when you need to target them.
Also see:
How to send one to one message using Firebase Messaging
Sending message to custom user using firebase
Send Firebase Cloud Messaging notification to users by user property
how to send data message to user segment From Rest API

Sending Firebase Cloud Message using UID of user

I want to build an Android app that allows a user to send notification and data messages to other users. I've started using Firebase only recently, and Firebase Cloud Messaging is still pretty confusing to me.
I have already implemented sending a message to a specific device using the Firebase Instance Id. However, in my app, a user can log out and log into their accounts using different devices, so this isn't really what I want. I read the documentation and it's pretty confusing, they mention sending messages to user groups, and topics (which only apps can subscribe to, not users).
Is there a way to send a push notification directly to another user or a group of users using only their UIDs? If not, is there any other way I can implement this?

I did it storing the FCM Token in a device structure by user. When the user login, add the deviceData to the userToken structure. You need clear deviceData when the user logout. This way, you will only send notifications to logged devices.
Ex (This is not like mine structure, but it can help you to wondering a good way to do this):
-userToken
-idUser1
-device
-idDevice1
-fcmToken: "xxxxx"
-idDevice2
-fcmToken: "YYYYY"
Hope that I helped you

Alright, so to make sure this works across multiple devices when a user logs in, I just make the device subscribe to a topic with the name equal to the user's UID. Now if I want to send a notification to a user, I just send an FCM message on the topic with the name equal to the user's UID!
Example: If my UID is equal to "asdf", whenever I login using multiple devices, each of the devices automatically subscribes to the topic with name "asdf". So now, if I send an FCM from the server on this topic, all the devices from which I am logged on to obtain this notification.

Push Notification to Specific Logged In User using Firebase/Batch

I'm building an app that allows the user to create events and add people to those events. It stores the event and certain user data (email and display name) in a Firebase database.
What I'm trying to do is send a notification to a specific user when another user adds them to an event. I've tried looking at the documentation for both Firebase Notifications/Cloud Messaging and Batch, but I can't find a way to send the notification to a single user, rather than an entire group.
How do I go about doing this? I'm hoping to avoid storing the notification in the Firebase DB and setting up a servlet backend that queries the DB repeatedly.
Edit: If I do have to make a Java Servlet backend for this, can someone tell me how I would code it?

I think you can do that by specifying the device token when sending the notification using console or using post request to FCM server. But unfortunately you have to handle every single device token manually by yourself (get it from the device when it register to FCM, and save it to your own DB somewhere).
If you use console, you can put the token on "FCM registration token" field under target -> single device.
If you use post request, you can make a request like this
{
"data": {"my_custom_key" : "my_custom_value"},
"registration_ids": ["your-device-token","your-device2-token"]
}

Batch.com provides a simpler API named Transactional API to send a notification to one or more users identified by their User ID, Firebase UID etc. as you probably don't want to deal with the complexity of APNS push tokens or GCM registration ids yourself. Contrary to FCM, you will get a complete analytics view (eg: open-rate) on those notifications.
You can trigger push notifications directly from your app code by using our Swift client for the Transactional API or by coding your own HTTP client (it's a standard POST request with a JSON body). We even have a client for Node.js if you decide to trigger the notifications from a server.
And if you are using Firebase, we have a specific documentation to plug Firebase with Batch.

Android Authentication and GCM Push notifications

I'm looking to create for my app some authentication. This will basically consist of a user registering (preferably with their google account, although not necessary) and providing a username that is then sent to my server and then having the ability to log in. I then from there would like to be able for the client app to communicate with my server by sending data and receiving push notifications via GCM (google cloud messaging). It is important that the server is able to send a push notification directly to a certain user not to all registered devices.
Would someone be able to point me in the right direction for what I must do? I've had a look at a few tutorials but what I've seen has always sent messages to all registered devices not to a specific user.
Some extra information about the app:
-The client app (user) will need to send a piece of information to the server. This information will also include the user that it needs to be sent to. Once the server receives the piece of information it should send a push notification through GCM to the specified user's client app.
I'm clueless as to how I need to go about setting up the authentication system, any help would be very appreciated!
Thank you very much,
Daniel

Offcourse you can send push notifications to selected users. This process would roughly comprise the following steps:
1) send the User's GCM registration id to your own server along with a unique user id (what ever id you have assigned to that user; could be email or sim id or something like that). Save it in your database.
2) To send Push notifications to selected users, choose users from the database based on some criteria, retrieve their GCM registration ids from the database and forward them the GCM server.
but there is one important thing you must handle. GCM registration ids could change e.g if user uninstalls and re-installs the application. You must update you corresponding database entry in that case.