在firestore中使用snapshot.count的最有效方法？

Question

I have a project storing user response data in firestore, which I want to regularly query to return count results on. ie. "how many users who chose X also chose Y". These are all chosen from a collection full of 'per-user' documents that contain their choices.

The (only) result I want for this usage is the total number of users who meet the condition, which I can get through snapshot.Count .

But if I have say, 1000 users who all meet the positive condition, does that count as 1000 reads? If so, is there a way of limiting that? I don't want to read the data, I just want the count...

Any steer on this would be really appreciated!

Thanks in advance

Answer 1

But if I have say, 1000 users who all meet the positive condition, does that count as 1000 reads?

Yes.

If so, is there a way of limiting that?

No. Firestore doesn't have any aggregation type queries like count, avg, min, max, etc.

I don't want to read the data, I just want the count.

Then you're going to have to keep a running count of documents (as they are added or deleted) in another document. You can read that one document to get the count.