在flutter中使用fromMap映射firebase文档中的嵌套对象

class Address {
  final String street;
  final String city;
  
  Address({required this.street, required this.city});
}

class User {
  final String name;
  final int age;
  final Address address;
  
  User({required this.name, required this.age, required this.address});
}

class User {
  // ...

  static User fromMap(Map<String, dynamic> map) {
    return User(
      name: map['name'],
      age: map['age'],
      address: Address.fromMap(map['address']),
    );
  }
}

class Address {
  // ...
  
  static Address fromMap(Map<String, dynamic> map) {
    return Address(
      street: map['street'],
      city: map['city'],
    );
  }
}

Map<String, dynamic> userData = {
  'name': 'John Doe',
  'age': 25,
  'address': {
    'street': '123 Main St',
    'city': 'New York',
  },
};

User user = User.fromMap(userData);
print(user.name); // 输出：John Doe
print(user.age); // 输出：25
print(user.address.street); // 输出：123 Main St
print(user.address.city); // 输出：New York