[Ignore] atbt discerning Insert/Update

[7CMiguel]

I need a way to discern between Insert/Update so some attbt dont get updated.
public class User
{
[Ignore]
public int id{ get; set; }
public string name{ get; set; }
[IgnoreUpdate]
public DateTime CreatedAt { get; set; }
[IgnoreUpdate]
public int CreatedBy { get; set; }
[IgnoreInsert]
public DateTime? ModifiedAt { get; set; }
[IgnoreInsert]
public int? ModifiedBy { get; set; }
}
Something like that