ASP.NET Core IdentityUser relations - asp.net-core

Question

How can I add a related object to the database?
My IdentityUser:
public class ApplicationUser : IdentityUser
{
public ICollection<Todo> Todos { get; set; }
}
My Todo model:
public class Todo
{
public int Id { get; set; }
public string Name { get; set; }
public ApplicationUser User { get; set; }
}
I have a WebAPI like /api/todos.
[HttpPost]
public async Task<IActionResult> Post([FromBody]string name)
{
var user = await _userManager.GetUserAsync(User);
// _db is IdentityDbContext that I use
var newTodo = new Todo() { Name = "do the laundry" }; // Do I have to specify the user like User = user?
_db.Todos.Add(newTodo);
await _db.SaveChangesAsync();
return CreatedAt(...);
}
Question: Am I doing it right? Do I have to pass the user to the new Todo item?
Can I somehow add the todo like that?:
user.Todos.Add(newTodo);
But how would I save it?

Answer 1

Add the User:
var user = await _userManager.GetUserAsync(User);
var newTodo = new Todo() { Name = "do the laundry", User = user };
_db.Todos.Add(newTodo);
await _db.SaveChangesAsync();
or add to the user and update it:
var user = await _userManager.GetUserAsync(User);
var newTodo = new Todo() { Name = "do the laundry" };
user.Todos.Add(newTodo);
_db.Users.Update(user);
await _db.SaveChangesAsync();
Either way should be fine.