code: def _get_related_exporter(self, related_obj, column):
          
          result = column.get('sqla_xls_exporter')
          if result is None:
              worksheet = self.book.create_sheet(
                  title=column.get('label', 'default title')
              )
              result = column['sqla_xls_exporter'] = SqlaXlsExporter(
                  related_obj.__class__,
                  worksheet=worksheet
              )
          return result
docs: returns an SqlaXlsExporter for the given related object and stores it in
          the column object as a cache