[c#] Update Row if it Exists Else Insert Logic with Entity Framework

Ladislav's answer was close but I had to made a couple of modifications to get this to work in EF6 (database-first). I extended my data context with my on AddOrUpdate method and so far this appears to be working well with detached objects:

using System.Data.Entity;

[....]

public partial class MyDBEntities {

  public void AddOrUpdate(MyDBEntities ctx, DbSet set, Object obj, long ID) {
      if (ID != 0) {
          set.Attach(obj);
          ctx.Entry(obj).State = EntityState.Modified;
      }
      else {
          set.Add(obj);
      }
  }
[....]