Firebase Functions - push notification when new document is created

Question

I have the following Firestore DB structure:

users
  $USER_ID
     notifications
       $DOC1
       $DOC2
       $DOC3

I want to push a new notification when a document is created at the user notification collection.

It should be something like this, but I don't know of any way to this for each $UID:

exports.newSubscriberNotification = functions.firestore
  .document('users/$UID/notifications')
  .onCreate(async event => {

How can I use Firebase Functions to do this? If there is no way, any suggestions for a workaround?

Answer 1

You should use the following code to trigger your Cloud Function:

    exports.newSubscriberNotification = functions.firestore
        .document('users/{userId}/notifications/{docId}')
        .onCreate((snap, context) => {
    
          //You get the values of the newly created doc as follows:
          const newValue = snap.data();
          console.log(newValue);
    
          //You get the parameters as follows:
          const userId = context.params.userId;
          //console.log(userId);
    
          const docId = context.params.docId;
          //console.log(docId);
    
          // You perform here the notification sending
        });

For the code for the notification sending, have a look at this official Firebase Cloud Function sample: https://github.com/firebase/functions-samples/blob/master/fcm-notifications/functions/index.js