Handle POST request.

def post(self, receiver_id=None):
        """Handle POST request."""
        try:
            user_id = request.oauth.access_token.user_id
        except AttributeError:
            user_id = current_user.get_id()

        event = Event.create(
            receiver_id=receiver_id,
            user_id=user_id
        )
        db.session.add(event)
        db.session.commit()

        # db.session.begin(subtransactions=True)
        event.process()
        db.session.commit()
        return make_response(event)