Multi Row Update Trigger - sql

Question

I've got this trigger:
CREATE TRIGGER tgr_passenger_flight
ON Flight
AFTER UPDATE
AS
BEGIN
IF ##ROWCOUNT= 0 RETURN
SET NOCOUNT ON
BEGIN TRY
IF EXISTS
(SELECT 1
FROM inserted I inner join PassengerForFlight PV ON I.flightnumber= PV.flightnumber)
BEGIN
;THROW 50000, 'Cannot update, Passenger is linked to flight',1
END
END TRY
BEGIN CATCH
;THROW
END CATCH
END
It works perfectly for one row update. But when i updated multi rows it failed.
What am I doing wrong? Do I have to change the join with PassengerForFlight? or must I also work with Deleted pseudo table because its a after update trigger?
Edit:
When i run this update-statement:
UPDATE Flight
SET gatecode = 'B'
WHERE flightcode = 'KL'
I've get the following message :
Thats correct, but this update statement touch two different flightnumbers. One thats not exist in PassengerForFlight and one that exists in PassengerForFlight.
What i want is:
1 row(s) affected and then the error message

Answer 1

There's nothing wrong with your JOIN. The problem is that you used IF EXISTS(). What you coded is: "if there is ANY row in the INSERTED table that exists in the PassengerForFlight table, then throw an error.
Since you're throwing an error, the trigger will rollback any transaction that it is participating in.
One way to do what you want is change this to an INSTEAD OF trigger, and to PRINT a message instead of throwing an error.
Your current code's philosophy is "let the UPDATE happen, and if certain condition exists, throw an error and roll it back." This can only happen in a way that affects the entire UPDATE (all rows).
I suggest a philosophy, of "Instead of the requested UPDATE, only UPDATE those rows that meet a certain condition. If any rows in the requested UPDATE didn't meet that condition, then give the user a message."