Cloud Firestore collection count

Question

Is it possible to count how many items a collection has using the new Firebase database, Cloud Firestore?

If so, how do I do that?

Answer 1

Solution using pagination with offset & limit:

public int collectionCount(String collection) {
        Integer page = 0;
        List snaps = new ArrayList<>();
        findDocsByPage(collection, page, snaps);
        return snaps.size();
    }

public void findDocsByPage(String collection, Integer page, 
                           List snaps) {
    try {
        Integer limit = 26000;
        FieldPath[] selectedFields = new FieldPath[] { FieldPath.of("id") };
        List snapshotPage;
        snapshotPage = fireStore()
                        .collection(collection)
                        .select(selectedFields)
                        .offset(page * limit)
                        .limit(limit)
                        .get().get().getDocuments();    
        if (snapshotPage.size() > 0) {
            snaps.addAll(snapshotPage);
            page++;
            findDocsByPage(collection, page, snaps);
        }
    } catch (InterruptedException | ExecutionException e) {
        e.printStackTrace();
    }
}

• findDocsPage it's a recursive method to find all pages of collection

• selectedFields for otimize query and get only id field instead full body of document

• limit max size of each query page

• page define inicial page for pagination

From the tests I did it worked well for collections with up to approximately 120k records!