UserClass.cs

public class User
{
  public string Email {get; set;}
  public string FirstName {get; set;}
  public string LastName {get; set;}
  public string Password {get; set;}
  public int Id {get; set;]
  
  public void Validate(bool isUpdate = false)
  {
    if(isUpdate && Id <= 0)
      throw new InvalidUserIdException();
      
    if(string.IsNullOrWhiteSpace(Email))
        throw new InvalidEmailException();
      
      if(!new Regex("^[A-Za-z]\w{6,}[A-Za-z]$").IsMatch(Password))
        throw new InvalidPasswordException();
    
      if(string.IsNullOrWhiteSpace(FirstName) || string.IsNullOrWhiteSpace(Lastame))
        throw new InvalidNameException();
  }
  
  public void Update(User newUser)
  {
      Email = newUser.Email;
      FirstName = newUser.FirstName;
      LastName = newUser.LastName;
      Password = newUser.Password;
  }
}

public class UserController : Controller
{
    [HttpPost]
    public ActionResult Create(User newUser)
    {
      new UserLogic().Create(newUser);
      
      return View("UserCreated");      
    }
    
    [HttpPost]
    public ActionResult Update(User updateUser)
    {
      new UserLogc().Update(updateUser);
      
      return View("UserUpdated");
    }
}
 
public class UserLogic
{
  public void Create(User newUser)
  {    
      newUser.Validate();
      
      var repo = new UserRepository();
      repo.Create(newUser);
  }
  
  public void Update(User update)
  {
      update.Validate(true);
      
      var repo = new UserRepository();
      var currentUser = repo.GetById(update.Id);
      
     currentUser.Update(update);
      
      repo.Save(currentUser);
  }
}