Firebase Cloud Functions Error with CanonicalRegistrationTokenCount - firebase

Question

I am trying to send a signup notification to my app after registration and user has been saved in db. I am using firebase cloud functions for this purpose.
I have gotten the device token from firebaseinstanceidservice and saved that in the user's db with the path users/userid/deviceToken and referenced this path in the function like below code:
exports.sendNotification = functions.database.ref("users/{userId}/{instanceId_token}")
I have tried logging the devicetoken just to be sure but in cloud console, I keep getting other attributes for that log like : sendNotification
deviceToken name, sendNotification
deviceToken userId instead of the alphanumeric value saved in db. Is this path wrong?
Here's my full code:
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);
exports.sendNotification =
functions.database.ref("users/{userId}/{instanceId_token}")
.onWrite((changes, context) => {
const userId = context.params.userId;
console.log("user-id", userId);
const notificationToken = context.params.instanceId_token;
console.log("deviceToken", notificationToken);
var payload = {
data: {
title: "Welcome to My Group",
message: "You may have new messages"
}
};
return admin.messaging().sendToDevice(notificationToken, payload)
.then(function (response) {
return console.log("Successfully sent message: ", response);
})
.catch(function (error) {
return console.log("Error sending message: ", error);
})
});
Also, the function shows this mildly positive message, after the admin.messaging callback:
Successfully sent message: { results: [ { error: [Object] } ],
canonicalRegistrationTokenCount: 0,
failureCount: 1,
successCount: 0,
multicastId: 8880906162831350000 }
How do I resolve this, I am using an android client?
Here's my db structure:

Answer 1

You should trigger you function on the upper node, as follows. And access the instanceId_token through changes.after.val().
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);
exports.sendNotification =
functions.database.ref("users/{userId}")
.onWrite((changes, context) => {
const userId = context.params.userId;
console.log("user-id", userId);
const notificationToken = changes.after.val().instanceId_token;
console.log("deviceToken", notificationToken);
var payload = {
data: {
title: "Welcome to My Group",
message: "You may have new messages"
}
};
return admin.messaging().sendToDevice(notificationToken, payload)
.catch(function (error) {
console.log("Error sending message: ", error);
})
});
In case you add the instanceId_token ONLY AFTER having created the user, then you should trigger with onUpdate() (which "triggers when data is updated", while onWrite() "triggers when data is created, updated, or deleted").
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);
exports.sendNotification =
functions.database.ref("users/{userId}")
.onUpdate((changes, context) => {
const userId = context.params.userId;
console.log("user-id", userId);
const notificationToken = changes.after.val().instanceId_token;
console.log("deviceToken", notificationToken);
if (notificationToken === undefined) {
console.log("notificationToken === undefined");
return false;
} else {
var payload = {
data: {
title: "Welcome to My Group",
message: "You may have new messages"
}
};
return admin.messaging().sendToDevice(notificationToken, payload)
.catch(function (error) {
console.log("Error sending message: ", error);
})
}
});
Also note that you should not do
return admin.messaging().sendToDevice(notificationToken, payload)
.then(function (response) {
return console.log("Successfully sent message: ", response);
})
.catch(function (error) {
return console.log("Error sending message: ", error);
});
because in this case you are not returning a promise "that resolves when all the async work is done in the function". (see the answer of this question)
So just return the promise returned by sendToDevice (see doc), as follows:
return admin.messaging().sendToDevice(notificationToken, payload)
.catch(function (error) {
console.log("Error sending message: ", error); // here no return
});