Firebase Firestore Error: The operator '[]' isn't defined for the class 'Object'

Question

im learning how to connect flutter app to firebase from this video

https://youtu.be/ggYTQn4WVuw

For me everything is exactly the same, but in Android Studio there is an error.

error: The operator '[]' isn't defined for the type 'Object'. (undefined_operator at [firebase_test] lib\services\database.dart:24)

Code where is error:

List<Brew> _brewListFromSnapshot(QuerySnapshot snapshot) {
return snapshot.docs.map((doc) {
  return Brew(
    name: doc.data()['name'] ?? '',
    strength: doc.data()['strength'] ?? 0,
    sugars: doc.data()['sugars'] ?? '0',
  );
}).toList();}

Brew Class:

class Brew {
  final String name;
  final String sugars;
  final int strength;

  Brew({ this.name, this.sugars, this.strength });
}

Can someone help me fix this? Is this a problem with Android Studio?

Answer 1

You are using the latest Firestore dependency, version 2.0.0, which was released May 4th, 2021 days ago. There are breaking changes, read about them here.

"Add withConverter", From the documentation:

Add withConverter function to CollectionReference, DocumentReference and Query (#6015). This new method allows interacting with collections/documents in a type-safe way:

final modelsRef = FirebaseFirestore
     .instance
     .collection('models')
     .withConverter<Model>(
       fromFirestore: (snapshot, _) => Model.fromJson(snapshot.data()!),
       toFirestore: (model, _) => model.toJson(),
     );

 Future<void> main() async {
   // Writes now take a Model as parameter instead of a Map
   await modelsRef.add(Model());
   final Model model = await modelsRef.doc('123').get().then((s) => s.data());
 }

Or, you can use simply:

String name = snapshot.data.get('name');
//instead of 
String name = (snapshot.data.data() as Map<String,dynamic>)['name']

And if you want the entire map:

Map<String,dynamic> data = snapshot.data.data() as Map<String,dynamic>);
String name = data['name'] ?? '';

Answer 2

Use this:

doc.get('name') ?? '', 

Instead of:

doc.data()['name'] ?? '',

Answer 3

First solution:

Your Brew Class:

class Brew {
  final String name;
  final String sugars;
  final int strength;

  Brew({ this.name, this.sugars, this.strength });
  
  Brew.fromJson(Map<String, dynamic> json)
      : this(
          name: json['name'] as String,
          sugars: json['sugars'] as String,
          strength: json['strength'] as int,
        );

  Map<String, Object?> toJson() {
    return {
      'name': name,
      'sugars': sugars,
      'strength': strength,
    };
  }
}

Your service:

List<Brew> _brewListCollectionReference (CollectionReference<Map<String, dynamic>> collectionReference) {
  QuerySnapshot<Object?> snapshot = await collectionReference.withConverter<Brew>(
          fromFirestore: (snapshots, _ ) => Recipe.fromJson(snapshots.data()!),
          toFirestore: (brew, _ ) => brew.toJson(),
        ).get();
  return snapshot.docs.map((doc) => doc.data() as Brew).toList();
}

Note: Your "collectionReference" is the reference from your firebase collection.

For example: firestore.collection('brewCollection')

Second solution:

List<Brew> _brewListFromSnapshot(QuerySnapshot snapshot) {
return snapshot.docs.map((doc) {
  return Brew(
    name: doc['name'] ?? '',
    strength: doc['strength'] ?? 0,
    sugars: doc['sugars'] ?? '0',
  );
}).toList();}

Third solution:

List<Brew> _brewListFromSnapshot(QuerySnapshot snapshot) {
return snapshot.docs.map((doc) {
  return Brew(
    name: doc.get('name') ?? '',
    strength: doc.get('strength') ?? 0,
    sugars: doc.get('sugars') ?? '0',
  );
}).toList();}