Collection Listener 的 Firestore 计费

Question

I want to add a listener to my collection to trigger a function "getNewChats()" whenever a document is added to the collection.

I have the following listener in my initState:

 CollectionReference reference = Firestore.instance.collection('chats');

  @override
  void initState() {
    super.initState();
    getChats();

    reference.snapshots().listen((querySnapshot) {
      querySnapshot.documentChanges.forEach((change) {
        getNewChats();
      });
    });

My question is whether I will be charged for reading every document in the "chats" collection every time the init state is run or will I only be charged when there is a change in the collection like a document added?

If so, is there any way to only listen to the most recently added document so I'm not reading everything?

Answer 1

On the first invocation of the listener, you will be billed 1 read for each document in the collection. After that, for each document added or modified, you will be billed for that document, until the listener is removed.

If you don't want to read all the documents in the colleciton, you will need a filter on that document. If you want only documents after a certain point in time, you will need to add a timestamp field to each document, and filter on that field. Your all will need to know what timestamp to use for the query - Firestore will not keep track of that for you.