Merging stream in flutter firetore - firebase

Question

I am using two quires to fetch data from the firestore.
Query 1.
_firestore
.collection('chats')
.doc(getCurrentUser().uid)
.collection('chatUsers')
.orderBy('timestamp');
with all the querysnapshot document from query 1. I am fetching last message and document id, and displaying the last message in listTile. With document id i am passing the id to fetch other data from other collection like name photo etc.
Query 2.
Future<DocumentSnapshot> fetchUserData(String uid) async => await _firestore
.collection('users')
.doc(uid).get();
So for this I need to use nested stream builder. First stream builder to fetch all data. Second stream builder to fetch user requested data from all data. what will be the best approach?
This is how i am using query 1 in my widgets for the query 2 I have to implement it inside the ListView.builder which will be the nested stream. please guide me with the best approach to this.
SafeArea(
child: Scaffold(
body: StreamBuilder<QuerySnapshot>(
stream: _fetchUserChatRoom.snapshots(),
builder:
(BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
if (snapshot.hasData) {
return _tiles(snapshot.data.docs);
} else if (snapshot.hasError) {
return Icon(Icons.error_outline);
} else {
return CircularProgressIndicator();
}
}),
),
);
}
Widget _tiles(List<QueryDocumentSnapshot> docs) {
return ListView.builder(
itemCount: docs.length,
itemBuilder: (BuildContext context, int index) {
var data = ChatModel.fromMap(docs[index].data());
return GestureDetector(
onTap: () => Navigator.of(context).push(MaterialPageRoute(
builder: (_) => ChatScreen(uid: docs[index].id))),
child: ListTile(
leading: CircleAvatar(),
title: Text(data.message),
subtitle: Text(data.timestamp.toString()),
trailing: Text('time'),
),
);
});

Answer 1

You can either use async and await in your ListView.builder, however, I imaging this could slowdown you app and cause a lot of firestore calls.
Widget _tiles(List<QueryDocumentSnapshot> docs) {
return ListView.builder(
itemCount: docs.length,
itemBuilder: (BuildContext context, int index) async {
var data = ChatModel.fromMap(docs[index].data());
var userData = await fetchUserData(data[index].uid);
return GestureDetector(
onTap: () => Navigator.of(context).push(MaterialPageRoute(
builder: (_) => ChatScreen(uid: docs[index].id))),
child: ListTile(
leading: CircleAvatar(),
title: Text(data.message),
subtitle: Text(data.timestamp.toString()),
trailing: Text('time'),
),
);
});
Other options (which I use) is to use a Provider class with all the contacts. You can fill the Provider when the app initializes with all the users in your firestore. After that you can use each user data anywhere in your app.