Flutter firebase，使用一个文档中的引用调用另一个文档

Question

I am using MultiProvider Stream with a database service with the firebase calls and a data model and using to and fromJson.

I am calling the Firestore User in my main file, and have a wrapper to call the user's document which holds the reference to the company they belong to, once the user data is retrieved we then call the company document in a userType screen, I then use the reference and pass it to the getter of the company document, but the document is being called before the document ref is passed.

I have tried to change the Stream to a Future but then I get an error on Provider.

Database Service

 Stream<Companies> streamCompanies() {
_userRef.get().then((DocumentSnapshot documentSnapshot) {
  if (documentSnapshot.exists) {
    print('HERE IS THE SNAPSHOT');
    print(documentSnapshot.get('companyID'));
    thisUserCompany = documentSnapshot.get('companyID');
  }
});
debugPrint('Database Service => GETTING COMPANY STREAM');
debugPrint(thisUserCompany);
return _database
    .collection('companies')
    .doc(thisUserCompany)
    .snapshots()
    .map(
      (snapshot) =>
          Companies.fromJson(snapshot.data() as Map<String, dynamic>),
    );

}

Comapnies Class

class Companies {
  final String uid;
  final String companyName;
  final String logoForPDF;

  Companies ({required this.uid, required this.companyName,
  required this.logoForPDF});

  Companies.fromJson(Map<String, dynamic> json)
      : uid = json['uid'],
        companyName = json['companyName'],
        logoForPDF = json['logoForPDF'];

  Map<String, dynamic> toJson() => {
        'uid': uid,
        'companyName': companyName,
        'logoForPDF': logoForPDF,
      };
      factory Companies.initialData() {
    return Companies(
      uid: 'Loading',
      companyName: 'Loading',
      logoForPDF: 'Loading',
    );
  }
}

MultiProvider

class HomeScreen extends StatelessWidget {
  const HomeScreen({super.key});

  @override
  Widget build(BuildContext context) {
    final user = Provider.of<UserData?>(context);
    return user != null
        ? MultiProvider(providers: [
            StreamProvider<Companies?>.value(
                initialData: Companies.initialData(),
                value: user != null
                    ? DatabaseService(uid: user.uid, companyID: user.companyID)
                        .streamCompanies()
                    : null),
          ], child: const ProfileSelector())
        : const CircularProgressIndicator();
  }
}

Answer 1

Ok so a little more perseverance I now have this working but I do not know if this is the correct way of doing this.

In my database file, I have changed the code to the following

  Stream<Companies> streamCompanies() async* {
    await _userRef.get().then((DocumentSnapshot documentSnapshot) {
      if (documentSnapshot.exists) {
        thisUserCompany = documentSnapshot.get('companyID');
      }
    });
     yield* _database
            .collection('companies')
            .doc(thisUserCompany)
            .snapshots()
            .map((snapshot) =>
                  Companies.fromJson(snapshot.data() as Map<String, dynamic>),
                );
  }