Flutter Firestore pagination - google-cloud-firestore

Question

I'm trying to paginate by using Firestore and I read the document and it implement like this in Swift
let first = db.collection("cities")
.order(by: "population")
.limit(to: 25)
first.addSnapshotListener { (snapshot, error) in
guard let snapshot = snapshot else {
print("Error retrieving cities: \(error.debugDescription)")
return
}
guard let lastSnapshot = snapshot.documents.last else {
// The collection is empty.
return
}
// Construct a new query starting after this document,
// retrieving the next 25 cities.
let next = db.collection("cities")
.order(by: "population")
.start(afterDocument: lastSnapshot)
// Use the query for pagination.
// ...
}
Just for practice, I tried fetched three documents and if button tapped, fetch one more document.
Firestore.instance.collection('user').where('name', isEqualTo: 'Tom').orderBy('age').limit(3).getDocuments().then((snapshot) {
_lastDocument = snapshot.documents.last;
snapshot.documents.forEach((snap) {
print(snap.data);
});
});
After button tapped tried like this.
Firestore.instance.collection('user').where('name', isEqualTo: 'Tom').orderBy('age').startAfter(_lastDocument).limit(1).getDocuments().then((snapshot) {
snapshot.documents.forEach((snap) {
print(snap.data);
});
});
But console says this.
The following assertion was thrown while handling a gesture: type
'DocumentSnapshot' is not a subtype of type 'List[dynamic]'
Why do I have to pass list?
Does anyone know how to fix this?
UPDATE
I was able to paginate like so.
class PaginationExample extends StatefulWidget {
#override
_PaginationExampleState createState() => _PaginationExampleState();
}
class _PaginationExampleState extends State<PaginationExample> {
var _restaurants = <Restaurant>[];
var _nomore = false;
var _isFetching = false;
DocumentSnapshot _lastDocument;
ScrollController _controller;
void _fetchDocuments() async {
final QuerySnapshot querySnapshot = await Firestore.instance.collection('restaurants').orderBy('likes').limit(8).getDocuments();
// your logic here
}
Future<Null> _fetchFromLast() async {
final QuerySnapshot querySnapshot = await Firestore.instance.collection('restaurants').orderBy('likes').startAfter([_lastDocument['likes']]).limit(4).getDocuments();
if (querySnapshot.documents.length < 4) {
_nomore = true;
return;
}
_lastDocument = querySnapshot.documents.last;
for (final DocumentSnapshot snapshot in querySnapshot.documents) {
final Restaurant re = Restaurant(snapshot);
_restaurants.add(re);
}
setState(() {});
}
void _scrollListener() async {
if (_nomore) return;
if (_controller.position.pixels == _controller.position.maxScrollExtent && _isFetching == false) {
_isFetching = true;
await _fetchFromLast();
_isFetching = false;
}
}
#override
void initState() {
_fetchDocuments();
_controller = new ScrollController()..addListener(_scrollListener);
super.initState();
}
#override
Widget build(BuildContext context) {
return Container(
);
}
}

Answer 1

There is an error here:
Firestore.instance.collection('user').where('name', isEqualTo: 'Tom').orderBy('age').startAfter(_lastDocument).limit(1).getDocuments().then((snapshot) {
snapshot.documents.forEach((snap) {
print(snap.data);
});
});
startAfter method expects a List value params and you are passing a DocumentSnapshot.
Takes a list of [values], creates and returns a new [Query] that
starts after the provided fields relative to the order of the query.
You could try something like this:
Firestore.instance.collection('user').where('name', isEqualTo: 'Tom').orderBy('age').startAfter([{'name': 'Tom'}]).limit(1).getDocuments().then((snapshot) {
snapshot.documents.forEach((snap) {
print(snap.data);
});
});

Answer 2

Paginate just with 2 attrubutes, itemBuilder and query using this package - paginate_firestore
For example,
PaginateFirestore(
itemBuilder: (context, documentSnapshot) => ListTile(
leading: CircleAvatar(child: Icon(Icons.person)),
title: Text(documentSnapshot.data['name']),
subtitle: Text(documentSnapshot.documentID),
),
// orderBy is compulsary to enable pagination
query: Firestore.instance.collection('users').orderBy('name'),
)

Answer 3

This works for me giving realtime pagination
defining functions to fetch data
import 'package:cloud_firestore/cloud_firestore.dart';
import '../../../core/constants/firebase_constants.dart';
class FirebaseProvider {
final FirebaseFirestore _firestore;
FirebaseProvider({required FirebaseFirestore firestore})
: _firestore = firestore;
CollectionReference get _posts =>
_firestore.collection(FirebaseConstants.postsCollection);
Future<List<DocumentSnapshot>> fetchFirstList(
String fromgst, String postType) async {
return (await _posts
.where("fromgst", isEqualTo: fromgst)
.where("postType", isEqualTo: postType)
.orderBy("date", descending: true)
.limit(5)
.get())
.docs;
}
Future<List<DocumentSnapshot>> fetchNextList(String fromgst, String postType,
List<DocumentSnapshot> documentList) async {
return (await _posts
.where("fromgst", isEqualTo: fromgst)
.where("postType", isEqualTo: postType)
.orderBy("date", descending: true)
.startAfterDocument(documentList[documentList.length - 1])
.limit(5)
.get())
.docs;
}
}
separate class to handle pagination
import 'dart:async';
import 'dart:io';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:growmore/features/home/repository/firebase_provider.dart';
import 'package:rxdart/rxdart.dart';
class PostListBloc {
List<DocumentSnapshot>? documentList;
bool showIndicator = false;
FirebaseProvider? firebaseProvider;
BehaviorSubject<List<DocumentSnapshot>>? postController;
BehaviorSubject<bool>? showIndicatorController;
PostListBloc() {
postController = BehaviorSubject<List<DocumentSnapshot>>();
showIndicatorController = BehaviorSubject<bool>();
firebaseProvider = FirebaseProvider(firestore: FirebaseFirestore.instance);
}
Stream get getShowIndicatorStream => showIndicatorController!.stream;
Stream<List<DocumentSnapshot>> get postStream => postController!.stream;
// This method will automatically fetch first 10 elements from the document list
Future fetchFirstList(String fromgst, String postType) async {
try {
documentList = await firebaseProvider?.fetchFirstList(fromgst, postType);
print("documentList$documentList");
postController?.sink.add(documentList!);
try {
if (documentList!.isEmpty) {
postController?.sink.addError("No Data Available");
}
} catch (e) {
print(e);
}
} on SocketException {
postController?.sink.addError(SocketException("No Internet Connection"));
} catch (e) {
print(e.toString());
postController?.sink.addError(e);
}
}
//This will automatically fetch the next 10 elements from the list
fetchNextPosts(String fromgst, String postType) async {
try {
updateIndicator(true);
List<DocumentSnapshot> newDocumentList = await firebaseProvider!
.fetchNextList(fromgst, postType, documentList!);
print('asca$newDocumentList');
documentList!.addAll(newDocumentList);
postController!.sink.add(documentList!);
try {
if (documentList!.isEmpty) {
postController!.sink.addError("No Data Available");
updateIndicator(false);
}
} catch (e) {
updateIndicator(false);
}
} on SocketException {
postController!.sink.addError(SocketException("No Internet Connection"));
updateIndicator(false);
} catch (e) {
updateIndicator(false);
print(e.toString());
postController!.sink.addError(e);
}
}
//For updating the indicator below every list and paginate*
updateIndicator(bool value) async {
showIndicator = value;
showIndicatorController!.sink.add(value);
}
void dispose() {
postController!.close();
showIndicatorController!.close();
}
}
the ui part
ScrollController controller = ScrollController();
#override
void initState() {
super.initState();
postListBloc = PostListBloc();
print("dvvfe${widget.fromgst}");
postListBloc!.fetchFirstList(widget.fromgst, widget.postType);
controller.addListener(_scrollListener);
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: StreamBuilder<List<DocumentSnapshot>>(
stream: postListBloc!.postStream,
builder: (context, snapshot) {
if (snapshot.data != null) {
return ListView.builder(
itemCount: snapshot.data?.length,
shrinkWrap: true,
controller: controller,
itemBuilder: (context, index) {
return Card(
child: Padding(
padding: const EdgeInsets.all(8.0),
child: ListTile(
title: Text(snapshot.data![index]['description']),
),
),
);
},
);
} else {
return const CircularProgressIndicator();
}
},
),
);
}
void _scrollListener() {
if (controller.offset >= controller.position.maxScrollExtent &&
!controller.position.outOfRange) {
print("Cavc$controller");
print("at the end of list");
postListBloc!.fetchNextPosts(widget.fromgst, widget.postType);
}
}
}
I found it not open source github repo