code: def forwards(apps, schema_editor):
      
      Event = apps.get_model('spectator_events', 'Event')
      ClassicalWorkSelection = apps.get_model(
                                  'spectator_events', 'ClassicalWorkSelection')
      DancePieceSelection = apps.get_model(
                                  'spectator_events', 'DancePieceSelection')
  
      for event in Event.objects.all():
  
          for work in event.classicalworks.all():
              selection = ClassicalWorkSelection(
                              classical_work=work,
                              event=event)
              selection.save()
  
          for piece in event.dancepieces.all():
              selection = DancePieceSelection(
                              dance_piece=piece,
                              event=event)
              selection.save()
docs: Copy the ClassicalWork and DancePiece data to use the new through models.