如何使用flutter对firestore文档及其子集合进行建模？

dependencies:
  cloud_firestore: ^2.5.3

import 'package:cloud_firestore/cloud_firestore.dart';

import 'package:firebase_core/firebase_core.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Firestore Demo',
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  final FirebaseFirestore firestore = FirebaseFirestore.instance;

  // ...
}

import 'package:json_annotation/json_annotation.dart';

part 'my_model.g.dart';

@JsonSerializable()
class MyModel {
  final String id;
  final String name;
  final int age;

  MyModel({required this.id, required this.name, required this.age});

  factory MyModel.fromJson(Map<String, dynamic> json) =>
      _$MyModelFromJson(json);

  Map<String, dynamic> toJson() => _$MyModelToJson(this);
}

class MyHomePage extends StatelessWidget {
  final FirebaseFirestore firestore = FirebaseFirestore.instance;
  final CollectionReference myCollection =
      FirebaseFirestore.instance.collection('my_collection');

  Future<void> addDocument() {
    final myModel = MyModel(id: '1', name: 'John', age: 25);
    final documentReference = myCollection.doc(myModel.id);
    return documentReference.set(myModel.toJson());
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Firestore Demo'),
      ),
      body: Center(
        child: ElevatedButton(
          child: Text('Add Document'),
          onPressed: addDocument,
        ),
      ),
    );
  }
}

class MyHomePage extends StatelessWidget {
  final FirebaseFirestore firestore = FirebaseFirestore.instance;
  final CollectionReference myCollection =
      FirebaseFirestore.instance.collection('my_collection');

  Future<void> queryDocuments() async {
    final querySnapshot = await myCollection.get();
    final documents = querySnapshot.docs;
    for (final document in documents) {
      final data = document.data();
      final myModel = MyModel.fromJson(data);
      print(myModel.name);
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Firestore Demo'),
      ),
      body: Center(
        child: ElevatedButton(
          child: Text('Query Documents'),
          onPressed: queryDocuments,
        ),
      ),
    );
  }
}