mapper.py 文件源码

def _iterate_polymorphic_properties(self, mappers=None):
        """Return an iterator of MapperProperty objects which will render into
        a SELECT."""
        if mappers is None:
            mappers = self._with_polymorphic_mappers

        if not mappers:
            for c in self.iterate_properties:
                yield c
        else:
            # in the polymorphic case, filter out discriminator columns
            # from other mappers, as these are sometimes dependent on that
            # mapper's polymorphic selectable (which we don't want rendered)
            for c in util.unique_list(
                chain(*[
                    list(mapper.iterate_properties) for mapper in
                    [self] + mappers
                ])
            ):
                if getattr(c, '_is_polymorphic_discriminator', False) and \
                        (self.polymorphic_on is None or
                         c.columns[0] is not self.polymorphic_on):
                    continue
                yield c