code: def _get_relationship_cell_val(self, obj, column):
          
          val = SqlaExporter._get_relationship_cell_val(self, obj, column)
          if val == "":
              related_key = column.get('related_key', None)
  
              if column['__col__'].uselist and related_key is None and \
                      self.is_root:
  
                  # on récupère les objets liés
                  key = column['key']
                  related_objects = getattr(obj, key, None)
                  if not related_objects:
                      return ""
                  else:
                      exporter = self._get_related_exporter(
                          related_objects[0],
                          column,
                      )
                      for rel_obj in related_objects:
                          exporter.add_row(rel_obj)
  
          return val
docs: Return the value to insert in a relationship cell
          Handle the case of complex related datas we want to handle