code: def obj_deref(ref):
      
      from indico_livesync.models.queue import EntryType
      if ref['type'] == EntryType.category:
          return Category.get_one(ref['category_id'])
      elif ref['type'] == EntryType.event:
          return Event.get_one(ref['event_id'])
      elif ref['type'] == EntryType.session:
          return Session.get_one(ref['session_id'])
      elif ref['type'] == EntryType.contribution:
          return Contribution.get_one(ref['contrib_id'])
      elif ref['type'] == EntryType.subcontribution:
          return SubContribution.get_one(ref['subcontrib_id'])
      else:
          raise ValueError('Unexpected object type: {}'.format(ref['type']))
docs: Returns the object identified by `ref`