firebase - 如何在 Flutter 中连接两个 Firestore 集合中的数据？

Question

我在 Flutter 中有一个使用 Firestore 的聊天应用程序，并且我有两个主要集合:

• chats，以自动 ID 为键，并具有 message、timestamp 和 uid 字段.
• users，以 uid 为键，并具有 name 字段

在我的应用程序中，我使用以下小部件显示消息列表(来自 messages 集合):

class ChatList extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    var messagesSnapshot = Firestore.instance.collection("chat").orderBy("timestamp", descending: true).snapshots();
    var streamBuilder = StreamBuilder<QuerySnapshot>(
          stream: messagesSnapshot,
          builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> querySnapshot) {
            if (querySnapshot.hasError)
              return new Text('Error: ${querySnapshot.error}');
            switch (querySnapshot.connectionState) {
              case ConnectionState.waiting: return new Text("Loading...");
              default:
                return new ListView(
                  children: querySnapshot.data.documents.map((DocumentSnapshot doc) {
                    return new ListTile(
                      title: new Text(doc['message']),
                      subtitle: new Text(DateTime.fromMillisecondsSinceEpoch(doc['timestamp']).toString()),
                    );
                  }).toList()
                );
            }
          }
        );
        return streamBuilder;
  }
}

但现在我想显示每条消息的用户名(来自 users 集合)。

我通常称之为客户端连接，尽管我不确定 Flutter 是否有具体的名称。

我找到了一种方法来执行此操作(我已在下面发布)，但想知道是否有另一种/更好/更惯用的方法在 Flutter 中执行此类操作。

那么:在 Flutter 中查找上述结构中每条消息的用户名的惯用方法是什么？

Answer 1

你可以像这样用 RxDart 做到这一点.. https://pub.dev/packages/rxdart

import 'package:rxdart/rxdart.dart';

class Messages {
  final String messages;
  final DateTime timestamp;
  final String uid;
  final DocumentReference reference;

  Messages.fromMap(Map<String, dynamic> map, {this.reference})
      : messages = map['messages'],
        timestamp = (map['timestamp'] as Timestamp)?.toDate(),
        uid = map['uid'];

  Messages.fromSnapshot(DocumentSnapshot snapshot)
      : this.fromMap(snapshot.data, reference: snapshot.reference);

  @override
  String toString() {
    return 'Messages{messages: $messages, timestamp: $timestamp, uid: $uid, reference: $reference}';
  }
}

class Users {
  final String name;
  final DocumentReference reference;

  Users.fromMap(Map<String, dynamic> map, {this.reference})
      : name = map['name'];

  Users.fromSnapshot(DocumentSnapshot snapshot)
      : this.fromMap(snapshot.data, reference: snapshot.reference);

  @override
  String toString() {
    return 'Users{name: $name, reference: $reference}';
  }
}

class CombineStream {
  final Messages messages;
  final Users users;

  CombineStream(this.messages, this.users);
}

Stream<List<CombineStream>> _combineStream;

@override
  void initState() {
    super.initState();
    _combineStream = Observable(Firestore.instance
        .collection('chat')
        .orderBy("timestamp", descending: true)
        .snapshots())
        .map((convert) {
      return convert.documents.map((f) {

        Stream<Messages> messages = Observable.just(f)
            .map<Messages>((document) => Messages.fromSnapshot(document));

        Stream<Users> user = Firestore.instance
            .collection("users")
            .document(f.data['uid'])
            .snapshots()
            .map<Users>((document) => Users.fromSnapshot(document));

        return Observable.combineLatest2(
            messages, user, (messages, user) => CombineStream(messages, user));
      });
    }).switchMap((observables) {
      return observables.length > 0
          ? Observable.combineLatestList(observables)
          : Observable.just([]);
    })
}

对于 rxdart 0.23.x

@override
      void initState() {
        super.initState();
        _combineStream = Firestore.instance
            .collection('chat')
            .orderBy("timestamp", descending: true)
            .snapshots()
            .map((convert) {
          return convert.documents.map((f) {

            Stream<Messages> messages = Stream.value(f)
                .map<Messages>((document) => Messages.fromSnapshot(document));

            Stream<Users> user = Firestore.instance
                .collection("users")
                .document(f.data['uid'])
                .snapshots()
                .map<Users>((document) => Users.fromSnapshot(document));

            return Rx.combineLatest2(
                messages, user, (messages, user) => CombineStream(messages, user));
          });
        }).switchMap((observables) {
          return observables.length > 0
              ? Rx.combineLatestList(observables)
              : Stream.value([]);
        })
    }