Cloud Functions and Firestore: Using Promise.all() to track multiple documetn modifications

Question

I use a callable Cloud function for creating a new user. For this user, multiple documents in Cloud Firestore are created.

I do not want to store only parts of the data, if one promise (document creation fails), but completely undo the registration, so I use Promise.all(documentCreationPromisses)

So my question is if it is still possible that some documents are created and others are not, although I use Promise.all() ?

Answer 1

Promise.all() returns a promise that tells you if all of the other promises succeeded, or if any one of them failed. It can certainly resolve with a partial set of successes, and there was a failure, you would have to check each individual promise to find out which ones succeeded or failed.

If you are modifying a bunch of documents in Firestore, and you require that all of the modifications either fully succeed, otherwise nothing happens (a full rollback), then you should use a batch write or transaction . With a batch writes and transactions, everything must succeed, or the entire batch fails. The single returned promise from that batch will tell you what happened.