Conference-app-2020: Thumbs-up function

[takahirom]

Kind (Required)

• Proposal / Discussion

  Overview (Required)

• We are showing thumbs-up instead of a session survey.

• We have set up the necessary Firestore rules for it.
• Please let us know if you have any missing rules or security issues.

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    match /confsched/2020 {
...
      match /sessions/{sessionId} {
        match /{allSubcollections=**} {
          allow create
        }
        // Allow to increment only the 'shards' field and only by 1.
        match /thumbsup_counters/{counterId} {
          allow get;
          allow write: if request.resource.data.keys() == ["shards"]
                         && (resource == null || request.resource.data.shards ==
                         resource.data.shards + 1);
        }
      }
    }
  }
}

• I think that the user can press the button any number of times. (Cannot be canceled.) Like medium crap.
• Regarding the creation of Firestore documents for sessions and counters, we are thinking of creating a Firestore document if there is no document from the application.

https://www.figma.com/file/4r9becvhDy3GfXaXex8E8d/App?node-id=21%3A289

| now | design |
|---|---|
| | |

## Links

• https://firebase.google.com/docs/firestore/solutions/counters

[mkeeda]

Can I challenge this issue ? 🙋

[takahirom]

Thank you! Please ask if you have anything 🔥

[mkeeda]

@takahirom
I would like to avoid to post to database for release.
The firestore which specified android-base/arc/debug/google-services.json is test database for develop, isn't it?

[takahirom]

@mkeeda Yes. That google-services.json is for develop 👍

[mkeeda]

memo

• The app collects to thumbs-up count of each user.
  confsched/2020/sessions/${sessionId}/thumbsup_counters/${userId}/shards/${shardsId}
  
  
  
  • The app creates a thumbsup_counters document when a user taps a thumbs-up button at first, because no counter of the user.
  
  
• Session Detail view show a thumbs-up count of a current user.
• DroidKaigi staffs collect a thumbs-up count of all users of each session.

[takahirom]

👀

[takahirom]

@mkeeda
confsched/2020/sessions/${sessionId}/thumbsup_counters/${counterId}/shards/1
How about sharing data with other users in this way?

[mkeeda]

@takahirom
I'm thinking to share data with other users, but I don't understand what to mean /thumbsup_counters/${counterId}/.
Why is multiple counters in thumbs-up collection?
Are the single thumbs-up counter of each session some problems, like confsched/2020/sessions/${sessionId}/thumbsup_counter/shards/${shardId}?

[mkeeda]

Are the single thumbs-up counter of each session some problems, like confsched/2020/sessions/${sessionId}/thumbsup_counter/shards/${shardId}?

Sorry, I did not notice this document of firestore.

Notice the alternating pattern of collections and documents. Your collections and documents must always follow this pattern. You cannot reference a collection in a collection or a document in a document.
https://firebase.google.com/docs/firestore/data-model?hl=en

.../thumbsup_counter/shards/${shardId} is collection in collection; .../collection/collection/document, so it's wrong setting.

[takahirom]

sessions/${sessionId}/thumbsup_counter/${shardId}
Probably we can remove like this?👀
I forgot why counterId is exists🤔🤔

[mkeeda]

@takahirom
Thank you🙏
I summarized the plans for sharing thumbs-up counts with all users.

Plan1: multiple counter

sessions/${sessionId}/thumbsup_counters/${userId}/shards/${shardsId}

• The app sums up thumbs-up count of all users, and displays.
• DroidKaigi staffs can check thumbs-up counts of each user. (not needed?)
• Counting cost increases with number of user * number of shard.

Plan2: single counter

sessions/${sessionId}/thumbsup_counter/${shardId}

• It's a simple implementation If counts of each user is not needed.
• Counting cost increases with number of shard.
• I still not check to be able implement this data model hierarchy.

[takahirom]

I want to try Plan2.
Like this.

sessions/${sessionId}/thumbsup_counter/1
                   shards : 9
sessions/${sessionId}/thumbsup_counter/2
                   shards : 11
sessions/${sessionId}/thumbsup_counter/3
                   shards : 10

[mkeeda]

OK 🙆
I'll fix the code as soon as possible.

[mkeeda]

After tapped thumbs-up button, the app should update the thumbs-up count.
Can I use the realtime update function with firestore?
I think that the app is able to update automatically the count when other users tap thumbs-up button of the same session. 🤔

Get realtime updates with Cloud Firestore  |  Firebase
https://firebase.google.com/docs/firestore/query-data/listen?hl=en

And I want to implement extensions for Kotlin Coroutines Flow if I adopt the realtime update. 🤔🤔

[takahirom]

I think so too. 👀
The favorite actually does the same thing except that there are multiple shards.
https://github.com/droidkaigi/conference-app-2020/blob/master/data/firestore/src/main/java/io/github/droidkaigi/confsched2020/data/firestore/internal/FirestoreImpl.kt#L38

[mkeeda]

Oh, sorry.
I missed it.😉
Thanks!!

[mkeeda]

@takahirom
I'm debugging to retrieve shards of thumbs-up counter.
I caught a permission error like this.

2020-02-02 03:05:28.280 4036-4106/io.github.droidkaigi.confsched2020.debug W/Firestore: (20.2.0) [Firestore]: Listen for Query(confsched/2020/sessions/155510/thumbsup_counter order by __name__) failed: Status{code=PERMISSION_DENIED, description=Missing or insufficient permissions., cause=null}
2020-02-02 03:05:28.499 4036-4036/io.github.droidkaigi.confsched2020.debug E/AndroidRuntime: FATAL EXCEPTION: main
    Process: io.github.droidkaigi.confsched2020.debug, PID: 4036
    com.google.firebase.firestore.FirebaseFirestoreException: PERMISSION_DENIED: Missing or insufficient permissions.
        at com.google.firebase.firestore.util.Util.exceptionFromStatus(com.google.firebase:firebase-firestore@@20.2.0:121)
...

While, I probably successed to create shards.
Could you show the security rules of firestore after changing into the single counter way?

[takahirom]

I will check today!

[mkeeda]

Security rules of /thumbsup_counters/{counterId} needs allow read.

• The app has to retrieve all shards of thumbsup_counters but allow get allows only single document read requests.
• allow list allows multiple document read requests.
• allow read includes get and list

New rules↓
https://github.com/DroidKaigi/conference-app-2020/pull/626#issuecomment-581129891

Discussion of changing rules ↓
https://twitter.com/mk_mkee/status/1223922969124040704?s=20

Thank you takahirom san!

[mkeeda]

When does the app show outlined button?

1. When user has never tap thumbs-up button of the session.
2. When thumbs-up count is zero
   

Now the app show contained button if thumbs-up count is zero.

[takahirom]

I talked with designer 👍
0 = white
1 or more(all people) = blue.

[mkeeda]

Idea for reduce access to firestore

• Change the security rule that allow only +1 update to thumbs-up count
  
  
  
  • Takahirom san already changed it!
  
  

request.resource.data.shards > resource.data.shards &&
request.resource.data.shards < resource.data.shards + 51

• Only request to update the thumbs-up count if a particular timespan has passed
• If users press the thumbs-up button continuously, only 1 request updates to firestore with a particular timespan
• Control the stream using debounce operator like Rx
• We can reduce number of shards too

Idea for users to feel repeated taps

• Show the user's tapping count separately from the all count of the session
• This idea is Inspired medium's crap