def __init__(self, expression, separator, distinct=False, ordering=None, **extra):
        self.separator = separator
        super(Sql_GroupConcat, self).__init__(expression,
                                              distinct='DISTINCT ' if distinct else '',
                                              ordering=' ORDER BY %s' % ordering if ordering is not None else '',
                                              separator=' SEPARATOR "%s"' % separator,
                                              output_field=CharField(),
                                              **extra)