code: def compute_to_fields(self, to_fields):
          
          # for problem in trim_join, we must try to give the fields in a consistent order with others models...
          # see #26515 at  https://code.djangoproject.com/ticket/26515
  
          return OrderedDict(
              (k, (v if isinstance(v, CompositePart) else LocalFieldValue(v)))
              for k, v in (to_fields.items() if isinstance(to_fields, dict) else zip(to_fields, to_fields))
          )
docs: compute the to_fields parameterse to make it uniformly a dict of CompositePart
          :param set[unicode]|dict[unicode, unicode] to_fields: the list/dict of fields to match
          :return: the well formated to_field containing only subclasses of CompositePart
          :rtype: dict[str, CompositePart]