CRUD Methods for single Model (not a list) with Provider - flutter

Question

How can I define methods(functions) for a single model that is not a list with Flutter's Provider? For example, I have made 4 functions for a Model that is a list:
List<User> _userList = [];
List<User> get userList => _userList;
//method for getiing and setting the list of users
setUserList(List<User> list) {
_userList = list;
notifyListeners();
}
// method for removing a single user
deleteUser(User list) {
_userList.remove(list);
notifyListeners();
}
//adding a new user
addUser(User list) {
_userList.add(list);
notifyListeners();
}
//updating the specific user
updateUser(User user) {
_userList [_userList.indexWhere((element) => element.id == user.id)] = user;
notifyListeners();
}
These all work fine (at least I think they work when I tested them :D) when it's a list of users, but how can I define these methods when it is a single object/item (single User) and not a list? The .add(), remove(), are methods that are available when there is a list, but not when there is a single item. What is the best approach for these CRUD model methods? The 'Read' is similar when it is a list:
User get user => _user;
//method for getting the user data
setUser(User user) {
_user = user;
notifyListeners();
}
but how I define the rest of the CRUD model like create(add), update and delete for a single model and not a list?

Answer 1

There is really not much difference when you are managing a list or a single item - just you will have methods that work on the single item. You do not show it above, but you should wrap your methods in a class (a "service") that maintains the data.
Here is an example authentication service that creates and deletes a User:
class AuthService with ChangeNotifier {
User _user;
User get user => _user;
Future<void> _authenticate(String email, String password,
[String name]) async {
// This is where you authenticate or register the user, and update the state
_user = User("dummy");
return Future<void>(() {});
}
Future<void> register(String name, String email, String password) async {
return _authenticate(email, password, name);
}
Future<void> login(String email, String password) async {
return _authenticate(email, password);
}
Future<void> logout() async {
_user = null;
notifyListeners();
return Future<void>(() {});
}
}
If it is not clear please ask in the comments.