docs: def import_orm(self):
          #TODO: check docstring
          """ Import ORM classes for oedb access depending on input in config in
          self.config which is loaded from 'config_db_tables.cfg'
          
          Returns
          -------
          int
              Descr #TODO check type
          """
  
          orm = {}
  
          data_source = self.config['input_data_source']['input_data']
          mv_grid_districts_name = self.config[data_source]['mv_grid_districts']
          mv_stations_name = self.config[data_source]['mv_stations']
          lv_load_areas_name = self.config[data_source]['lv_load_areas']
          lv_grid_district_name = self.config[data_source]['lv_grid_district']
          lv_stations_name = self.config[data_source]['lv_stations']
          conv_generators_name = self.config[data_source]['conv_generators']
          re_generators_name = self.config[data_source]['re_generators']
  
          from egoio.db_tables import model_draft as orm_model_draft, \
              supply as orm_supply, \
              demand as orm_demand, \
              grid as orm_grid
  
          if data_source == 'model_draft':
              orm['orm_mv_grid_districts'] = orm_model_draft.__getattribute__(mv_grid_districts_name)
              orm['orm_mv_stations'] = orm_model_draft.__getattribute__(mv_stations_name)
              orm['orm_lv_load_areas'] = orm_model_draft.__getattribute__(lv_load_areas_name)
              orm['orm_lv_grid_district'] = orm_model_draft.__getattribute__(lv_grid_district_name)
              orm['orm_lv_stations'] = orm_model_draft.__getattribute__(lv_stations_name)
              orm['orm_conv_generators'] = orm_model_draft.__getattribute__(conv_generators_name)
              orm['orm_re_generators'] = orm_model_draft.__getattribute__(re_generators_name)
              orm['version_condition_mvgd'] = 1 == 1
              orm['version_condition_mv_stations'] = 1 == 1
              orm['version_condition_la'] = 1 == 1
              orm['version_condition_lvgd'] = 1 == 1
              orm['version_condition_mvlvst'] = 1 == 1
              orm['version_condition_re'] = 1 == 1
              orm['version_condition_conv'] = 1 == 1
          elif data_source == 'versioned':
              orm['orm_mv_grid_districts'] = orm_grid.__getattribute__(mv_grid_districts_name)
              orm['orm_mv_stations'] = orm_grid.__getattribute__(mv_stations_name)
              orm['orm_lv_load_areas'] = orm_demand.__getattribute__(lv_load_areas_name)
              orm['orm_lv_grid_district'] = orm_grid.__getattribute__(lv_grid_district_name)
              orm['orm_lv_stations'] = orm_grid.__getattribute__(lv_stations_name)
              orm['orm_conv_generators'] = orm_supply.__getattribute__(conv_generators_name)
              orm['orm_re_generators'] = orm_supply.__getattribute__(re_generators_name)
              orm['data_version'] = self.config[data_source]['version']
              orm['version_condition_mvgd'] =\
                  orm['orm_mv_grid_districts'].version == orm['data_version']
              orm['version_condition_mv_stations'] = \
                  orm['orm_mv_stations'].version == orm['data_version']
              orm['version_condition_la'] =\
                  orm['orm_lv_load_areas'].version == orm['data_version']
              orm['version_condition_lvgd'] =\
                  orm['orm_lv_grid_district'].version == orm['data_version']
              orm['version_condition_mvlvst'] =\
                  orm['orm_lv_stations'].version == orm['data_version']
              orm['version_condition_re'] =\
                  orm['orm_re_generators'].columns.version == orm['data_version']
              orm['version_condition_conv'] =\
                  orm['orm_conv_generators'].columns.version == orm['data_version']
          else:
              logger.error("Invalid data source {} provided. Please re-check the file "
                           "`config_db_tables.cfg`".format(data_source))
              raise NameError("{} is no valid data source!".format(data_source))
  
          return orm