str: Organisation Group ID

def organisation_group_id(self):
        """
        str: Organisation Group ID
        """
        self._validate()
        self._validate_for_organisation_group_id()

        parts = []
        parts.append(self.election_type)
        if self.subtype:
            parts.append(self.subtype)
        parts.append(self.organisation)
        parts.append(self.date)
        return ".".join(parts)