Trigger or Callback?

Question

Question

Evgeny Shvarov · Nov 13, 2017

#Database Transaction Processing #Object Data Model #ObjectScript #Caché

Hi, folks!

Consider I need to perform some logic which should fire because values of object properties has been changed.

Is there ANY reason for using class callbacks %OnBeforeSave or %OnAfterSave instead of Trigger?

Discussion (5)1

Log in or sign up to continue

Danny Wijnschenk · Nov 13, 2017

Since 2014.1 we have 'unified' Triggers in Caché : if you use 'Foreach = row/object' in your trigger, it will be called from SQL and Object operations, a lot easier to write common code :

Trigger T1 [Event = INSERT, Foreach = row/object
{

  //your code

}

See also in the docs : http://docs.intersystems.com/latest/csp/docbook/DocBook.UI.Page.cls?KEY=...

2 0

score 2 · Answer 1 · 2017-11-13T03:54:15-05:00

%On... callbacks are served and integrated into he OBJECT world and typically don't care about any Trigger.

Triggers live in the SQL TABLE world of your class, with a hand full off %-variables unknown at the Object side
~~and without an actual instance of object but directly writing to Globals.~~

Take a look to the generated .INT code of your class and see what you have at hands.
I always found it quite ambitious to attempt a common code of both sides when directly changing Objects or Tables.

Summary:
- for SQL access have Triggers
- for Object access have your %On* methods

Applies only before 2014.1 as pointed out.
But Trigger code doesn't look much better.

score 0 · Answer 2 · 2017-11-13T07:36:23-05:00

Thanks, I missed that leaving before

And I've seen the new generated code added to %Save()
It confirmed my feelings about %* ....

score 0 · Answer 3 · 2017-11-14T16:55:13-05:00

Thanks, Danny!

Actually, I raised already similar discussion but I still prefer object callbacks because of better code readability.

BTW, if I have both unified Trigger and OnBeforSave callback would they fire both?

And why don't we have unified ObjectScript callbacks?

score 0 · Answer 4 · 2017-11-15T04:34:17-05:00

SQL Code and it's style and methodology was there long before Objects in actual style where introduced. (feeling mid 90ties)
It was mainly kept for backward compatibility.
In Caché 5 (2002) they were a real parallel universe Object - SQL.
Later Computed + SQLcomputed Properties were for long time the only place for common code.