@api.onchange('event_id')
def _onchange_event_id(self):
    if (self.event_ticket_id and ((not self.event_id) or (self.event_id != self.event_ticket_id.event_id))):
        self.event_ticket_id = None
@api.onchange('event_id')
def _onchange_event_id(self):
    if (self.event_ticket_id and ((not self.event_id) or (self.event_id != self.event_ticket_id.event_id))):
        self.event_ticket_id = None