code: def _collect_relationship(self, main_infos, prop, result):
          
          # No handling of the uselist relationships for the moment
          # Maybe with indexes ? ( to see: on row add, append headers on the fly
          # if needed )
          if prop.uselist:
              # One to many
              pass
          else:
              if "related_key" in main_infos:
                  self._merge_many_to_one_field(main_infos, prop, result)
              else:
                  related_field_inspector = BaseSqlaInspector(prop.mapper)
                  main_infos_list = []
  
                  for column in related_field_inspector.get_columns_only():
                      infos = self._get_prop_infos(column)
                      if self._is_excluded(column, infos):
                          continue
  
                      infos['label'] = u"%s %s" % (
                          main_infos['label'], infos['label']
                      )
                      infos['__col__'] = main_infos['__col__']
                      infos['name'] = "%s %s" % (main_infos['name'], column.key)
                      infos['key'] = main_infos['key']
                      infos['related_key'] = column.key
                      main_infos_list.append(infos)
                  return main_infos_list
  
          return main_infos
docs: collect a relationship header:
  
          * One To many : if {'export': {'reletad_key': 'remote_attr'}} is
              provided, we take all the related objects and join their remote
              attr's value with commas
              If an index is provided, only the related element of index 'index'
              is retrieved and it's attr value is returned
              In case of excel exports, a specific sheet is generated by table
              (see excel.py for more details)
  
          * Many To One :
  
              If a related_key is provided, we remove the associated foreign key
              from the output (we collect its associated title) and only the given
              key of the associated object will be exported
              If no related_key is provided, we use the relationship's title as
              prefix and for each attribute of the related object, we add a column
  
          :param dict main_infos: The already collected datas about this column
          :param obj prop: The property mapper of the relationship
          :param list result: The actual collected headers
          :returns: a dict with the datas matching this header