code: def init(req, model):
      rels = model.relationships
      fields = model.all_fields
      params = req.get_param_as_list('sort') or [goldman.config.SORT]
      params = [Sortable(param.lower()) for param in params]
      for param in params:
          _validate_no_rels(param, rels)
          _validate_field(param, fields)
      return params