Error updating different Collection document using Cloud Function - firebase

Question

By using Cloud Functions, when a document from "users" collection is edited, the edited files should be updated in uploads collection wherever the user id is stored.
For the above requirement I am using the below function.
const functions = require('firebase-functions');
const admin = require('firebase-admin');
const settings = {
timestampsInSnapshots: true
};
admin.initializeApp();
admin.firestore().settings(settings);
var db = admin.firestore();
exports.updateUser = functions.firestore.document('users/{userId}')
.onUpdate((change, context) => {
var userId = context.params.userId;
const newValue = change.after.data();
const name = newValue.display_name;
var uploadsRef = db.collection('uploads');
uploadsRef.where('user.id', '==', userId).get().then((snapshot) => {
snapshot.docs.forEach(doc => {
doc.set({"display_name" : name}); //Set the new data
});
}).then((err)=> {
console.log(err)
});
});
When this executes, I get the below error in the logs.
TypeError: doc.set is not a function
at snapshot.docs.forEach.doc (/user_code/index.js:31:21)
at Array.forEach (native)
at uploadsRef.where.get.then (/user_code/index.js:29:27)
at process._tickDomainCallback (internal/process/next_tick.js:135:7)
And also the below.
Unhandled rejection
How do I approach the problem? What is the best approach to deal with the snapshots document updates?

Answer 1

When you do a get() on a Query object, it will yield a
QuerySnapshot object. When you use its docs property, you're iterating an array of QuerySnapshotDocument objects that contain all the data from the matched documents. It looks like you're assuming that a QuerySnapshotDocument object has a set() method, but you can see from the linked API docs that it does not.
If you want to write back to a document identified in a QuerySnapshotDocument, use its ref property to get a DocumentReference object that does have a set() method.
doc.ref.set({"display_name" : name}); //Set the new data
Bear in mind that if you make this change, it will run, but may not update all the documents, because you're also ignoring the promise returned by the set() method. You'll need to collect all those promises into an array and use Promise.all() to generate a new promise to return from the function. This is necessary to help Cloud Functions know when all the asynchronous work is complete.