Firestore集合查询在Flutter中作为流 [英] Firestore collection query as stream in flutter

问题描述

我正在尝试从集合中查询一些文档，该查询应侦听查询的文档中所做的更改，因此我需要一个流.我正在关注(在Dart/Flutter中)

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));
  }

(对象Collection会在其构造函数中设置ref的路径，例如:ref = db.collection($ path)，然后地图会生成结果模型)

然后，我在stream上使用StreamBuilder调用上述方法，并在builder上检查是否有snapshot.hasData.但是它一直在加载，snapshot.hasData一直为假.我在这里做什么错了?

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?

1. 我的firestore安全规则包含:

1. My firestore security rules contain:

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

删除每个where和orderBy时，也找不到任何内容.并且在requests-collection

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

当尝试仅从请求集合中以流形式查询1个文档时，他确实找到了结果

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

是因为我应该将索引添加到我的Firestore索引中吗?但这并不能解决我的第一个问题，即使没有where和orderBy，它也无法获取任何数据

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

推荐答案

我已经写了一个简单的示例，它看起来像您正在尝试执行的操作，但是缺少了listen()方法:

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));
  }
);

这只是如何从Firestore流中获取数据并在StreamBuilder上使用它的一个示例:

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;
        }),
      ),
    );
  }

} 

这篇关于Firestore集合查询在Flutter中作为流的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！