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:

Answer 1

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.