Firebase Cloud Functions called multiple times

Question

Hello my firebase cloud function gets called multiple times when I don't put in check for previous.exists(). I get multiple push notifications.

if (!event.data.exists()){
    return;
}
if (event.data.previous.exists()){
    return;
}

But when I check for it i don't get push notification. Here is the not working code: What should I change?

exports.sendShoppingListInvitationNotification = functions.database.ref('/invites/{id}/').onWrite(event => {
//get the snapshot of the written data
const snapshot = event.data;  

if (!event.data.exists()){
    return;
}
if (event.data.previous.exists()){
    return;
}

    //get snapshot values
    console.log(snapshot.key);
const receiptToken = snapshot.child('receiptFcmToken').val();
const senderName = snapshot.child('senderNickname').val();
const inviteMessage = snapshot.child('inviteMessage').val();
const senderImage = snapshot.child('senderProfileImageURL').val();


//create Notification
const payload = {
    notification: {
        title: `Invitation from ${senderName}`,
        body:  `${inviteMessage}`,
        icon: `${senderImage}`,
        badge: '1',
        sound: 'default',
    }
};               

//send a notification to firends token   
return admin.messaging().sendToDevice(receiptToken, payload).then(response => { 
     console.log("Successfully sent message:", response);
 }).catch((err) => {
    console.log(err);
});   
});

I don't get error message on cloud console.

This is the firebase structure:

score 8 · Answer 1 · answered Aug 27 '17 at 18:32

8

Seems like it shouldn’t be called multiple times unless you’re doing multiple writes to that location. Try using .onCreate instead of .onWriteif you only want to send a notification on the first write to the path. Then you won’t need that check for previous data. See the documentation here which outlines the different database triggers.

answered Aug 27 '17 at 18:32

Jen Person

7,356
22
30

1

great Idea. I just watched your tutorial. Its an honor to get answerd by an expert. – Peter Sypek Aug 27 '17 at 18:48
Sad I just don't get my data now. The onCreate function delivers null for the receiptFcmToken. Error: Registration token(s) provided to sendToDevice() must be a non-empty string or a non-empty array. – Peter Sypek Aug 27 '17 at 19:24
I think i got a idea when i call onWrite my function executes on each childnode when it is added. The onCreate delivers the an empty node just when it is created and before childs added I think. But how i get the child values. Iam little confused. – Peter Sypek Aug 27 '17 at 19:44
How are you adding the data to the database? I tested out your code and it works as expected. However, if you are adding some of the children of each `id` one at a time or in groups rather than as one child, the function will be called for each addition. What's the code that adds the data to the database? – Jen Person Aug 27 '17 at 22:31
Thank you @Jen thats the solution. I die not write the data at once. I need to use the setValues method with an array of key value pairs. – Peter Sypek Aug 28 '17 at 03:29
There is one question left I want to ask you. Would you suggest to use a thread safe array for firebase because of often async data calls? – Peter Sypek Aug 28 '17 at 03:43
2

Seems assuming cloud firestore triggered functions will only execute one time is not safe: See here https://stackoverflow.com/questions/48735862/firestore-cloud-functions-oncreate-ondelete-sometimes-immediately-triggered-twic and here: https://stackoverflow.com/questions/49217120/how-to-make-idempotent-aggregation-in-cloud-functions/50860068#50860068 I had this issue with an aggregation. Really think docs should be changed to highlight this: https://firebase.google.com/docs/firestore/solutions/aggregation#solution_cloud_functions Could happen rarely and be painful bug if not idempotent. – cdock Sep 15 '18 at 02:17
Echoing @cdock, this happens to me on a regular basis. I observed it as soon as i switched function region to match the firestore region. – Alex Suzuki Apr 30 '19 at 19:17
Moving the function back to the default region us-central1 helped, have not seen any duplicate invocations so far. Not a solution, but probably still helpful to some. – Alex Suzuki Apr 30 '19 at 19:24

Firebase Cloud Functions called multiple times

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