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.

It might help people answer if you posted an example document from your collection (so we can see the schema). — RedBrogdon

vbandrade vbandrade · Accepted Answer · 2018-06-15T01:02:23

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();

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

4 Answers