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

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.

Solution 1:

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();

Solution 2:

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>