How do you load array and object from Cloud Firestore in Flutter

Question

I have a class that has several embedded arrays as well as a couple of objects. I'm using Flutter and can't figure out how to read/write to Cloud Firestore.

I can read/write data members that are default types like String and Int. Here is the constructor I'm trying to use to instantiate an object from a DocumentSnapshot:

 class GameReview {    String name;    int howPopular;    List<String> reviewers;  }   class ItemCount {    int itemType;    int count;     ItemCount.fromMap(Map<dynamic, dynamic> data)        : itemType = data['itemType'],          count = data['count'];  }   class GameRecord {    // Header members    String documentID;    String name;    int creationTimestamp;    List<int> ratings = new List<int>();    List<String> players = new List<String>();    GameReview gameReview;    List<ItemCount> itemCounts = new List<ItemCount>();     GameRecord.fromSnapshot(DocumentSnapshot snapshot)        : documentID = snapshot.documentID,          name = snapshot['name'],          creationTimestamp = snapshot['creationTimestamp'],          ratings = snapshot['ratings'], // ERROR on run          players = snapshot['players'], // ERROR on run          gameReview = snapshot['gameReview']; // ERROR on run          itemCount = ????  } 

It works until I add the last 3 members (ratings, players and gameReview). This should be obvious but none the less, it eludes me.

Help!

UPDATE: Here is a sample of the document stored in Cloud Firestore. This is stored in a single document. In other words, I'm not using sub-collections for the embedded objects. I put it into a JSON format for clarity. I hope this helps.

 {    "documentID": "asd8didjeurkff3",    "name": "My Game Record",    "creationTimestamp": 1235434,    "ratings": [      4,      2012,      4    ],    "players": [      "Fred",      "Sue",      "John"    ],    "gameReview": {      "name": "Review 1",      "howPopular": 5,      "reviewers": [        "Bob",        "Hanna",        "George"      ]    },   "itemCounts": [      {        "itemType": 2,        "count": 3      },      {        "itemType": 1,        "count": 2      }    ]  } 

UPDATE 2: I didn't put in the whole class definition because I thought it would be obvious to me how to do the rest but alas that was not the case.

I have a list of objects that I want to load.vbandrade's answer is BANG on but I can't quite figure out how I'm supposed to create the list of objects. List.from(...) is looking for an iterator, not a created class. I'm sure it's some variation of creating a new object and then adding it to a list but I'm a little confused. (see edits in class above, specifically, the "itemCounts" member.

Answer 1

If you came here because of List<dynamic> is not of type List<someType> error while reading data from firestore, you can just use List.castFrom

Example: List<String> cards = List.castFrom(cardsListFromFirebase);

Checkout Flutter firebase, List<dynamic> is not of type List<String>

Answer 2

load the list from the array and let the framework take care of type casting.

an object is simply a map, like you wrote in your Json. I also use named constructor. ((still learning and dont know how to use the static constructor @ganapat mentioned))

here´s the working code. I kept firebase auth out and used the StreamBuilder widget.

import 'dart:async'; import 'package:cloud_firestore/cloud_firestore.dart'; import 'package:flutter/material.dart'; import 'model/firebase_auth_service.dart';  void main() async {   runApp(new MyApp()); }  class MyApp extends StatelessWidget {   final firebaseAuth = new FirebaseAuthService();    MyApp() {     firebaseAuth.anonymousLogin();   }    @override   Widget build(BuildContext context) {     return MaterialApp(         home: Scaffold(             body: Center(                 child: FlatButton(       color: Colors.amber,       child: Column(         mainAxisSize: MainAxisSize.min,         children: <Widget>[           Text("get Game Record"),           StreamBuilder<GameRecord>(             stream: getGame(),             builder: (BuildContext c, AsyncSnapshot<GameRecord> data) {               if (data?.data == null) return Text("Error");                GameRecord r = data.data;                return Text("${r.creationTimestamp} + ${r.name}");             },           ),         ],       ),       onPressed: () {         getGame();       },     ))));   } }  Stream<GameRecord> getGame() {   return Firestore.instance       .collection("games")       .document("zZJKQOuuoYVgsyhJJAgc")       .get()       .then((snapshot) {     try {       return GameRecord.fromSnapshot(snapshot);     } catch (e) {       print(e);       return null;     }   }).asStream(); }  class GameReview {   String name;   int howPopular;   List<String> reviewers;    GameReview.fromMap(Map<dynamic, dynamic> data)       : name = data["name"],         howPopular = data["howPopular"],         reviewers = List.from(data['reviewers']); }  class GameRecord {   // Header members   String documentID;   String name;   int creationTimestamp;   List<int> ratings = new List<int>();   List<String> players = new List<String>();   GameReview gameReview;    GameRecord.fromSnapshot(DocumentSnapshot snapshot)       : documentID = snapshot.documentID,         name = snapshot['name'],         creationTimestamp = snapshot['creationTimestamp'],         ratings = List.from(snapshot['ratings']),         players = List.from(snapshot['players']),         gameReview = GameReview.fromMap(snapshot['gameReview']); } 

snapshot['itemCount'] is an array of objects. map each item in that array to an ItemCount object and return as a List:

    itemCounts = snapshot['itemCount'].map<ItemCount>((item) {       return ItemCount.fromMap(item);     }).toList();