answer add :

@api.multi
    def write(self, vals):
    	result = super(StockAlert, self).write(vals)
    	for record in result:
    		followers= []
    		if record.responsable_id.partner_id.id not in record.message_follower_ids.ids:
    			follower.append(record.responsable_id.partner_id.id)
    		record.message_subscribe(followers)
    	return result
    	
    @api.model
    def create(self, vals):
    	result = super(StockAlert, self).create(vals)
    	for record in result:
    		followers= []
    		if record.responsable_id.partner_id.id not in record.message_follower_ids.ids:
    			followers.append(record.responsable_id.partner_id.id)
    		record.message_subscribe(followers)
    	return result