Firestore 集合查询为 flutter 中的 stream

Question

I'm trying to query a few documents from a collection, this query should listen to changes made in the queried documents, so I'd need a stream. I'm doing following (in Dart/Flutter)

  Stream<List<MatchRequest>> _getNewMatches() {
    return Collection<MatchRequest>(path: 'requests')
        .ref
        .where('status', isNull: true)
        .where('users', arrayContains: ['$currentUid'])
        .orderBy('last_activity')
        .snapshots()
        .map((list) => list.documents.map(
            (doc) => Global.models[MatchRequest](doc.data) as MatchRequest));
  }

(The object Collection sets the path to the ref in it's constructor, eg: ref = db.collection($path) and the map makes a model of the results)

Then I'm using a StreamBuilder with stream invoking the method above and builder checking if snapshot.hasData. But it keeps loading, snapshot.hasData keeps being false. What am I doing wrong here?

EDIT:

1. My firestore security rules contain:

    match /requests/{requestId} { allow read: if isLoggedIn(); allow write: if isLoggedIn(); }

2. When removing every where and orderBy , it doesn't find anything as well. And there are documents present in the requests-collection

3. When trying to query only 1 document as a stream from the requests-collection, he does find the result

4. Is it because I should add indexes to my firestore indexes? But this won't solve my first problem which is that even without where and orderBy , it doesn't get any data

Answer 1

I've written a simple example of it seems to be like what you are trying to do but are missing the listen() method:

Firestore.instance.collection('collection')
  .where('field', isEqualTo: 'value')
  .orderBy('field')
  .snapshots()
  .listen((QuerySnapshot querySnapshot){
    querySnapshot.documents.forEach((document) => print(document));
  }
);

This is just an example of how you can take the data from a Firestore Stream and use it on a StreamBuilder:

class _MyHomePageState extends State<MyHomePage> {
  Stream dataList;

  @override
  void initState() {
    dataList = Firestore.instance.collection('collection')
      .where('field', isEqualTo: 'value')
      .orderBy('field')
      .snapshots();

    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: StreamBuilder(
          stream: dataList,
          builder: (context, asyncSnapshot) {
            if(asyncSnapshot.hasError)
              return Text('Error: ${asyncSnapshot.error}');

            switch (asyncSnapshot.connectionState) {
              case ConnectionState.none: return Text('No data');
              case ConnectionState.waiting: return Text('Awaiting...');
              case ConnectionState.active:
                return ListView(
                  children: asyncSnapshot.data.map((document) => Text(document['value'])),
                );
              break;
              case ConnectionState.done: return ListView(
                children: asyncSnapshot.data.map((document) => Text(document['value'])),
              );
              break;
            }
            return null;
        }),
      ),
    );
  }

} 

Answer 2

1. Multiple Documents

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: StreamBuilder<QuerySnapshot>(
          stream: FirebaseFirestore
                  .instance.
                  .collection('users') // 👈 Your desired collection name here
                  .snapshots(), 
          builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
            if (snapshot.hasError) {
              return const Text('Something went wrong');
            }
            if (snapshot.connectionState == ConnectionState.waiting) {
              return const Text("Loading");
            }
            return ListView(
                children: snapshot.data!.docs.map((DocumentSnapshot document) {
              Map<String, dynamic> data =
                  document.data()! as Map<String, dynamic>;
              return ListTile(
                title: Text(data['fullName']), // 👈 Your valid data here
              );
            }).toList());
          },
        ),
      ),
    );
  }

2. Single Document

 @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: StreamBuilder<DocumentSnapshot<Map<String, dynamic>>>(
          stream:  FirebaseFirestore
                   .instance
                   .collection('users')
                   .doc(FirebaseAuth.instance.currentUser!.uid) // 👈 Your document id change accordingly
                   .snapshots(), 
          builder:
              (BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
            if (snapshot.hasError) {
              return const Text('Something went wrong');
            }
            if (snapshot.connectionState == ConnectionState.waiting) {
              return const Text("Loading");
            }
            Map<String, dynamic> data =
                snapshot.data!.data()! as Map<String, dynamic>;
            return Text(data['fullName']); // 👈 your valid data here
          },
        ),
      ),
    );
  }

Also refer: How to use StreamBuilder and FutureBuilder for single and multiple documents