Add listener for collection changes

[matanmarciano]

Hello, how can I add a listener for collection changes?

[nbransby]

Using the snapshots flow, see https://github.com/GitLiveApp/firebase-kotlin-sdk#flows

[matanmarciano]

OK thanks, so I did something like:

suspend fun observeUsersChanged() {
    val firebaseFirestore : FirebaseFirestore = Firebase.firestore(Firebase.app)
    val usersCollection = firebaseFirestore.collection("Users")

    usersCollection.snapshots.collect {
        querySnapshot ->
        val documents = querySnapshot.documents
        // TODO: get list of my own 'User' object instead of list of DocumentSnapshot
    }
}

How can I get a list of my own 'User' object?

I know about data() method of document..but can I get list instead of use for each?

[matanmarciano]

And how can I get only the delta? it means-
if I implement a chat application, I want to listen to new messages, but only for the new message/s instead of getting all messages on each event

[matanmarciano]

@nbransby

[nbransby]

First question to ask yourself is how would you do it in firebase in general, once you have that answer I can help suggest best way to do it in the firebase-kotlin-sdk

[matanmarciano]

Im not sure how to do it generally because I'm start with firebase with your library...
I can try to explain what I am trying to implement.

I want to create a basic chat application:
Android app - Recycler view for the messages list
Kotlin multiplatform library for common chat code - here I want to implement the communication with Firestore (based your SDK).

So if I already have (for example) 100 messages in my chat..
I am sending a new message and I get 101 documents instead of only 1 new document..

the code for listening is:

override fun observeOnMessagesChanged() {
        CoroutineScope(GlobalScope.coroutineContext).launch {
            messagesCollection.snapshots.collect { querySnapshot ->
                querySnapshot.documents.forEach { documentSnapshot ->
                    val message = documentSnapshot.data<Message>()
                }
            }
        }
    }

[nbransby]

looks like you need docChanges() which we havent exposed yet https://firebase.google.com/docs/firestore/query-data/listen?authuser=0#view_changes_between_snapshots

You can create a feature request or even help us add it by creating a PR!

[matanmarciano]

OK I have opened a feature request here: #122
Hope to find a time to help you too sometimes

Thanks!