Adds the relationships (e.g. "event" or "attachments")
        that should be expanded with the $expand parameter
        Important: The ApiComponent using this should know how to handle this relationships.
            eg: Message knows how to handle attachments, and event (if it's an EventMessage).
        Important: When using expand on multi-value relationships a max of 20 items will be returned.
        :param str relationships: the relationships tuple to expand.
        :rtype: Query

def expand(self, *relationships):
        """ Adds the relationships (e.g. "event" or "attachments")
        that should be expanded with the $expand parameter
        Important: The ApiComponent using this should know how to handle this relationships.
            eg: Message knows how to handle attachments, and event (if it's an EventMessage).
        Important: When using expand on multi-value relationships a max of 20 items will be returned.
        :param str relationships: the relationships tuple to expand.
        :rtype: Query
        """

        for relationship in relationships:
            if relationship == 'event':
                relationship = '{}/event'.format(self.protocol.get_service_keyword('event_message_type'))
            self._expands.add(relationship)

        return self