title: Unique unchangeable id for core data object
body: <p>i'm making a small playlist app at the moment.</p>
  
  <p>i've made a playlistName entity which contain the name of the playlist.</p>
  
  <p>then i've made a song entity which contains all the songs in all the playlists. To know which song is in which playlist i've stored the ObjectID from the selected playlist object in an attribute called selectedRow.</p>
  
  <p>This is how i would do it in other language like PHP/SQL. The problem is here, that every time i run the app the playlists objectID seem to change. So the saved objectID in the song entity wont be the same as the playlist objectID when the app is restarted.</p>
  
  <p>How should i approach this issue? </p>