docs: def _put_into_indexes(self, obj):
          """
          Put publication into all indexes.
  
          Attr:
              obj (obj): Indexable object.
  
          Raises:
              UnindexableObject: When there is no index (property) which can be
                  used to index `obj` in database.
          """
          no_of_used_indexes = 0
          for field_name, db_index in list(self._get_db_fields(obj)):
              attr_value = getattr(obj, field_name)
  
              if attr_value is None:  # index only by set attributes
                  continue
  
              container = db_index.get(attr_value, None)
              if container is None:
                  container = OOTreeSet()
                  db_index[attr_value] = container
  
              container.insert(obj)
  
              no_of_used_indexes += 1
  
          # make sure that atleast one `attr_value` was used
          if no_of_used_indexes <= 0:
              raise UnindexableObject(
                  "You have to use atleast one of the identificators!"
              )