Cloud Function that moves documents between collection - google-cloud-firestore

Question

I have three collections: "past", today", and "future".
"today" collection is supposed to have only one document.
At midnight, I need to find in my "future" collection a document that has "next" field, or, if there is no such document, find one that have value in "number" field closest grater than value in "number" field of the document in my "today" collection. Then I need to move the "today"'s document into "past" collection, and also to move that found document from "future" collection to the "today" collection.
As far as I understand, there is no "move" method, so I have to use combination of deletes and creates which need to be done in one transaction.
I figured out how to do a "scheduler" part, but can't figure out how to code the rest (the actual moving of the documents).
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();
const firestore = admin.firestore();
exports.scheduledFunction = functions.pubsub.schedule('0 0 * * *')
.onRun((context) => {
//I need to move my documents...
});
Could you help me with the code, please?

Answer 1

It might me that you are looking for a documentation in a wrong place. Its not in the Firestore/Extend with cloud functions. Its in Firestore basic documentation, but you have to switch the code type to node-js. https://firebase.google.com/docs/firestore/query-data/order-limit-data
You have to collect data by two queries: in today and future collections.
By these queries you get the docs and its' data.
Than you just need to make a doc in past, delete and make new a doc (or rewrite the existing one) in today, and to delete in future.
There is how I would do it in a simple callable function:
exports.scheduledFunction = functions.pubsub.schedule('0 0 * * *')
.onRun(async (context) => {
try {
let queryToday = admin.firestore().collection('today'); //you can add .limit(1)
const todaySnapshot = await queryToday.get();
const todayDoc = todaySnapshot.docs[0];
const todayData = todayDoc.data();
const todayToPastRef = admin.firestore().doc(`past/${todayData.documentUid}`);
/* or how the id is stored? you can just call
const todayToPastRef = admin.firestore().collection('past').doc()
and it will be generated automatically
*/
const promises = [];
promises.push(todayToPastRef.set(todayData));
let queryFuture = admin.firestore().collection('future').orderBy('date').limit(1);
/*
or how is the date stored? Idk if firebase allows to query by Timestamp
you just want to fetch the closest date after today so the order is ascending
*/
const futureSnapshot = await queryFuture.get();
const futureDoc = futureSnapshot.docs[0];
const futureData = futureDoc.data();
const futureToTodayRef = admin.firestore().doc(`today/${futureData.documentUid}`);
promises.push(futureToTodayRef.set(todayData));
promises.push(futureDoc.ref.delete());
promises.push(todayDoc.ref.delete());
/*
or you can try to change today's doc data, but the id will remain the same
promises.push(todayDoc.ref.update(futureData))
*/
return Promise.all(promises); // function will be executed after all the promises are fullfilled or rejected
} catch (err) {
return Promise.reject(err);
}
});
Note that instead of .then() and .catch() im using async/await.
Use console.log() for debugging, and try VSCode, so you can inspect methods and properties on the objects, which is rly helpful
UPDATE:
Yes, you can do it with a batch. There is another example:
exports.scheduledFunction = functions.pubsub.schedule('0 0 * * *').onRun((context) => {
const db = admin.firestore();
let queryToday = db.collection('today');
let queryFuture = db.collection('future').orderBy('date').limit(1);
const batch = db.batch();
return queryToday
.get()
.then(todaySnapshot => {
const todayDoc = todaySnapshot.docs[0];
const todayData = todayDoc.data();
const todayToPastRef = db.doc(`past/${todayData.docUid}`);
batch.set(todayToPastRef, todayData);
batch.delete(todayDoc.ref);
return queryFuture.get();
})
.then(futureSnapshot => {
const futureDoc = futureSnapshot.docs[0];
const futureData = futureDoc.data();
const futureToTodayRef = db.doc(`today/${futureData.docUid}`);
batch.set(futureToTodayRef, futureData);
batch.delete(futureDoc.ref);
// now two operations are completed, you just can commit the batch
return batch.commit();
})
.catch(err => {
// if todaySnapshot or futureSnapshot were not fetched, batch wont be commited
// or, for example, if snapshots were empty
return Promise.reject(err)
});
});
You can also fetch documents in parallel with .getAll() or something like that. You should test and experiment