Re: Making Triggers Resilient -- RPG400-L


Hello,

(1) You must ensure that the triggered program has all objects it requires in the library list.

If at all possible, eliminate the need for other objects. (Aside from those that are part of the OS and therefore in the system portion of the library list.)

Personally, the triggers I've written don't use any other objects -- but I guess it depends on what the trigger does.

The next question that comes to mind is, "what objects are you having problems with?" Does your trigger need to call other programs? Make printouts? Reference other databases? Data queues?

Perhaps the best solution is to stop using the library list to locate the objects that your trigger depends on. If it needs a file, have it specify the library. If it calls a program, have it specify the library... I wouldn't recommend hard-coding the library, but you could create a configuration file or data area that the program could load the libraries from. Then, if you wanted to run on another library for some reason, you could easily change it.

(2) What happens if someone use UPDDTA without file ABC being in the library list, i.e. UPDDTA MYLIB/ABC.


As far as I can tell, this is the same question as (1).

(1) Placing the trigger program in the same library as the file it is triggered from.

I don't see how that helps you. Sure, if you assume the database is always accessed by library list, you'll be okay... but that's not always the case.

(2) Using a generic trigger program that sets the correct library list using either a job description or library list held in a common file linked to the library/file/member/trigger type/trigger time.

Nononono! Don't change the library list in a trigger... that would be really confusing for the user who sets her library list for a reason, and it's suddenly, magically, reverted back to the default one.

Just code your RPG program so that it doesn't use the library list to locate things! For example, on a program call, do this:

      C                   eval      Program = 'MYLIB/MYPGM'
      C                   CALL      Program
      C                   PARM                    FOO

Or, with a prototype:

     D Program         s             21A

     D MYPGM           PR                  EXTPGM('MYLIB/MYPGM')
     D   Parm1                       10A

      /free

          Program = 'MYLIB/MYPGM';
          callp MYPGM('FOO');
      /end-free

Or, with a file:

     FMYFILE    UF   E           K DISK    EXTFILE(LibFile)
     F                                     USROPN
     D LibFile         s             21A

     C                   eval      LibFile = 'MYLIB/MYFILE'
     C                   open      MYFILE

(Except, of course, load the library names from a configuration file or data area or something...)

That way, you don't have to change the library list (which affects other things) your changes only affect the trigger. You'll probably want to put the code that does this in your *INZSR so that you only have to do it once when the trigger first loads... doing it on each call could be expensive.

HTH