feat(firestore-counter): Create distributed_counter.dart

[Matrinica]

Translated from the TypeScript version

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[Matrinica]

@googlebot I signed it!

[Salakar]

cc @rrousselGit - would you remind reviewing this one? If you need more context feel free to ping me internally

[jhuleatt]

Thanks for your contribution @Matrinica! Do you have time to update your code to address @rrousselGit's comments? Once those suggestions are addressed, we can merge this PR

[dackers86]

Hi @Matrinica.

This PR has gone a little stale. Are you able to address the code suggestions above, we can then hopefully get this reviewed ahead of a release. Thanks!

[polarby]

@Matrinica Thanks for contributing, I was looking for that the whole time. It would be great if you could finish it for release, so people might be able to use it?! I am looking forward to it!

[polarby]

Here is how to use the package, which could be displayed at the firebase How this extension works under the Extension:

    import 'dart:async';
    import 'package:cloud_firestore/cloud_firestore.dart';
    import 'package:cloud_firestore/FirestoreCounter.dart'; // *this would be needed to be implemented*


    // somewhere in your app code initialize Firestore instance
    final db = FirebaseFirestore.instance;
    // create reference to the collection and the document you wish to use
    DocumentReference doc = db.collection("pages").doc("hello-world");


    // initialize FirestoreShardedCounter with the document and the property which will hold the counter value
    DistributedCounter visits = new DistributedCounter(doc, "visits");


    // to increment counter
    await visits.incrementBy(1);


    // make one time call to query total amount of visits
    int totalVisits = await visits.get();


    print("totalVisits: $totalVisits");


    // listen for updates
    StreamSubscription<int> registration =
        visits.onSnapshot().listen((totalVisits) {
      print("registration listen totalVisits: $totalVisits");
    });
    // clean up event listeners once finished
    registration.cancel();


    // if you don't mind counter delays, you can listen to the document directly.
    db.doc("pages/hello-world").snapshots().listen((querySnapshot) {
      // total page visits
      int totalVisits = querySnapshot.get("visits");
      print("onSnapshot totalVisits: $totalVisits");
    });

[rlee1990]

Any update on this?

[polarby]

@rlee1990 Quickfix (as this might need some time): Simply implement it yourself. This is just a library that would you would have access to when merged. All the code including the documentation is in this issue. Take the latest edits and use the package like this

[rlee1990]

@rlee1990 Quickfix (as this might need some time): Simply implement it yourself. This is just a library that would you would have access to when merged. All the code including the documentation is in this issue. Take the latest edits and use the package like this

Thanks will give it a try.

[rlee1990]

@PaulLVoelker I keep getting this error: Unhandled Exception: Null check operator used on a null value

Looks like This should be added: import 'package:uuid/uuid.dart'; var uuid = Uuid();

factory DistributedCounter(DocumentReference<Object?> doc, String field) {
    //Add init(uuid.v4());
    init(uuid.v4());
    final shardsRef = doc.collection(SHARD_COLLECTION_ID);
    Map<String, int> shards = {};
    shards[doc.path] = 0;
    shards[shardsRef.doc(shardId).path] = 0;
    shards[shardsRef.doc('\t' + shardId!.substring(0, 4)).path] = 0;
    shards[shardsRef.doc('\t\t' + shardId!.substring(0, 3)).path] = 0;
    shards[shardsRef.doc('\t\t\t' + shardId!.substring(0, 2)).path] = 0;
    shards[shardsRef.doc('\t\t\t\t' + shardId!.substring(0, 1)).path] = 0;
    Stream<int> snapshots = StreamGroup.mergeBroadcast<int>(shards.keys.map(
        (path) => doc.firestore
                .doc(path)
                .snapshots()
                .map<int>((DocumentSnapshot snap) {
              shards[snap.reference.path] = snap.exists ? snap.get(field) : 0;
              return shards.values.reduce((a, b) => a + b);
            })));
    return DistributedCounter._(doc, field, snapshots);
  }

[polarby]

Absolutely! Unfortunately, you need to install the package. I mentioned something like that here.

Is the error referring to the import? Or to the shardId!.substring(0, 4)).path?

[rlee1990]

To shardId!.substring(0, 4)).path once I added that it all was working.

[polarby]

@rlee1990 Great! Yea that's something the guys from firebase either need to import or find another solution. But for now, you have to use this package, as you somehow need a unique id. BTW: you could you use something with time

[dackers86]

@Matrinica Can you update and add the uuid package in the example that @polarby mentioned. Thanks!

[ymerdrengene]

Any status on this?

[submetu]

Hi guys, would be great if we can merge this PR :)

[pr-Mais]

Closing in favor of #1375.