Cloud firebase batch update - firebase

Question

I am trying to use a batch update to update a count within each snapshot. But it seems like the function doesnt even run. I know it has something to do with the second promise but I am not sure where.
import * as functions from 'firebase-functions';
import * as admin from 'firebase-admin';
export const replyCreated = functions
.firestore
.document(`/Reply/{replyId}`)
.onCreate((change: any, context: functions.EventContext) => {
const promises = [];
promises.push(admin.firestore().doc(`Challenge/${change.data().challenge_id}`).update({replyCount: admin.firestore.FieldValue.increment(1)}))
promises.push(admin.firestore()
.collection(`User`)
.where('following', 'array-contains', change.data().user_id).get().then((snapshot: any) => {
if (!snapshot.empty) {
const batch = admin.firestore().batch();
snapshot.forEach((doc: any) => {
const tempObject = doc.data()
console.log(`/Subscribed_Challenges/${tempObject.userId}/myChallenges/${change.data().challenge_id}`)
const myChallenge = admin.firestore().doc(`/Subscribed_Challenges/${tempObject.userId}/myChallenges/${change.data().challenge_id}`)
batch.update(myChallenge, {replyCount: admin.firestore.FieldValue.increment(1)})
})
return batch.commit().catch((err: any) => {
console.log('Batch Error', err)
});
}
else {
return Promise.resolve()
}
}))
return Promise.all(promises)
.then(() => {
return "upvote complete";
})
})

Answer 1

If I correctly understand you code, you don't need to use Promise.all() but you need to correctly chain the different Promises returned by the asynchronous Firestore methods.
The following should do the trick (untested):
export const replyCreated = functions
.firestore
.document(`/Reply/{replyId}`)
.onCreate((change: any, context: functions.EventContext) => {
return admin.firestore().doc(`Challenge/${change.data().challenge_id}`).update({ replyCount: admin.firestore.FieldValue.increment(1) })
.then(() => {
return admin.firestore()
.collection(`User`)
.where('following', 'array-contains', change.data().user_id).get()
})
.then((snapshot: any) => {
if (!snapshot.empty) {
const batch = admin.firestore().batch();
snapshot.forEach((doc: any) => {
const tempObject = doc.data()
console.log(`/Subscribed_Challenges/${tempObject.userId}/myChallenges/${change.data().challenge_id}`)
const myChallenge = admin.firestore().doc(`/Subscribed_Challenges/${tempObject.userId}/myChallenges/${change.data().challenge_id}`)
batch.update(myChallenge, { replyCount: admin.firestore.FieldValue.increment(1) })
})
return batch.commit()
}
else {
throw new Error('Snapshot empty')
}
})
.catch((err: any) => {
console.log('Error', err);
return null;
});
})
You would use Promise.all() if you need to execute a number of asynchronous methods (which return a Promise) in parallel. In your case (if I am not mistaking) the only case where you need to execute asynchronous methods in parallel is in the block where you use the batched write, therefore the parallel execution is executed by the batched write itself. For the other methods, it is more a sequential execution and you have to chain the promises with the then() method.