How to delete data from Firestore with cloud functions - node.js

Question

I'm writing a cloud functions in conjunction with google's Firestore database.
I'm trying to write recursive delete more data. I can't find the syntax for accessing and deleting data in other parts of the database.
The code I have already is below.
exports.deleteProject = functions.firestore.document('{userID}/projects/easy/{projectID}').onDelete(event => {
// Get an object representing the document prior to deletion
// e.g. {'name': 'Marie', 'age': 66}
// console.log(event)
// console.log(event.data)
console.log(event.data.previous.data())
var deletedValue = event.data.previous.data();
});
I found some info here but I don't have time to check through it atm, if I find something useful I'll amend the question.
https://firebase.google.com/docs/firestore/manage-data/delete-data?authuser=0

Answer 1

One can use below code to delete all the documents in a collection recursively.
This code worked perfectly for me.
Make sure you have JSON file of firebase credentials and firebase-admin installed.
const admin = require('firebase-admin');
const db = admin.firestore();
const serviceAccount = require('./PATH_TO_FIREBASE_CREDENTIALS.json');
admin.initializeApp({
credential: admin.credential.cert(serviceAccount)
});
deleteCollection(db, COLLECTION_NAME, NUMBER_OF_RECORDS)
async function deleteCollection(db, collectionPath, batchSize) {
const collectionRef = db.collection(collectionPath);
const query = collectionRef.orderBy('__name__').limit(batchSize);
return new Promise((resolve, reject) => {
deleteQueryBatch(db, query, resolve).catch(reject);
});
}
async function deleteQueryBatch(db, query, resolve) {
const snapshot = await query.get();
const batchSize = snapshot.size;
if (batchSize === 0) {
// When there are no documents left, we are done
resolve();
return;
}
// Delete documents in a batch
const batch = db.batch();
snapshot.docs.forEach((doc) => {
batch.delete(doc.ref);
});
await batch.commit();
// Recurse on the next process tick, to avoid
// exploding the stack.
process.nextTick(() => {
deleteQueryBatch(db, query, resolve);
});
}

Answer 2

The answer is that you must write a cloud function that deletes the data on its own and is trigger by the client. There isn't an efficient way to do it with client side. The method I use is I listen in the cloud function for the first delete and then fire the recursive.
Code to delete in node js:
db.collection("cities").document("DC").delete(