'query method for event sub-topics list
:param view_kwargs:
:return:'

def query(self, view_kwargs):

    query_ = self.session.query(EventSubTopic)
    if view_kwargs.get('event_topic_id'):
        event_topic = safe_query(self, EventTopic, 'id', view_kwargs['event_topic_id'], 'event_topic_id')
        query_ = query_.join(EventTopic).filter((EventTopic.id == event_topic.id))
    return query_
