CODEWITHSUNDEEP
firebasegoogle-cloud-firestore
Chen
Chen

Reputation: 980

Firestore count number of documents

If I have a Firestore document in the following structure:

enter image description here

In my web app, I would like to display the number of followers. If I just do a get() of the whole followers sub-collection. That will be costly in terms of read operations. I thought about the following solution:

Having a counter document and having a counter field that would be incremented every time a document is created inside the followers collection using cloud function. But there is the limit of one write per second per document for that counter. The idea to have a followers collection and each document for each follower is to avoid the one write per second limit (thanks to Doug Stevenson's blog: The top 10 things to know about Firestore when choosing a database for your app).

The only get around for that I can think of is to use distributed counter extension. But from I read so far, the counter only works with front-end SDK. Would I be able to use the extension in a cloud function or in a node.js backend to increase the followers counter?

Upvotes: 0

Views: 317

Answers (2)

Frank van Puffelen
Frank van Puffelen

Reputation: 600141

The "one write per document per second" is a guideline and not a hard rule, so I'd highly recommend not immediately getting hung up on that.

Then again, if you think you'll consistently need to count more than can be kept in a single document, your options are:

  1. Keep a distributed counter, as shown in the documentation on distributed counters.

  2. Keep the counter somewhere else. For example, I typically keep counters in Realtime Database, which has much higher write throughput (but lower read concurrency per shard).

Upvotes: 2

Doug Stevenson
Doug Stevenson

Reputation: 317968

But from I read so far, the counter only works with front-end SDK.

That's not true. The extension works for any query made to Firestore.

Would I be able to use the extension in a cloud function or in a node.js backend to increase the followers counter?

The extension works by monitoring documents added to and removed from the collection. It doesn't matter where the change comes from. You will still be able to use the computed counter from any code that's capable of querying the counter documents.

Upvotes: 1

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