CODEWITHSUNDEEP
firebasegoogle-cloud-firestore
Verdagon
Verdagon

Reputation: 2620

Can we not query collections inside transactions?

Looking at https://firebase.google.com/docs/reference/js/firebase.firestore.Transaction I see four methods: delete, set, get, update.

I was about to construct a lovely little collection query and pass it to .get, but I see the docs say that .get "Reads the document referenced by the provided DocumentReference."

It appears this means we cannot get a collection, or query a collection, with a Transaction object.

I could query those with the query's .get() method instead of the transaction's .get() method, but if the collection changes out from under me, the transaction will end up in an inconsistent state without retrying.

It seems I am hitting a wall here. Is my understanding correct? Can we not access collections inside a transaction in a consistent way?

Upvotes: 40

Views: 12178

Answers (2)

Doug Stevenson
Doug Stevenson

Reputation: 317477

Your understanding is correct. When using the web and mobile SDKs, you have to identify the individual documents that you would like to ensure will not change before your transaction is complete. If those documents come from a collection query ahead of time, fine. But think for a moment about how not-scalable it would be if you had to track every document in a (very large) collection in order to complete your transaction.

However, for backend SDKs, you can perform a query inside a transacction and effectively transact on all the documents that were returned by the query, up to the limit of number of documents in a transaction (500).

Upvotes: 33

JayCodist
JayCodist

Reputation: 2544

You can run queries (not just fetch single documents) in a transaction's get() method, but that's only for server execution. So if you really need to do that (say for maintaining denormalized data's consistency), you can put that code in a cloud function and make use of server-side transactions

Upvotes: 12

Related Questions