Utilities 400 NiSUG Trigger Presentation

Utilities 400 | System i Solutions | Using triggers to improve your business processes

Using triggers to improve
business processes
Steve Close
Utilities 400 Limited.

Your data, where, when and how you want it…


Triggers
- One of the most underused
features on the operating system

- Can cause a trigger to be
executed (“fired”!) whenever a
record is added, updated, deleted
or read from a file

- Triggers can call any program to
perform additional business logic


Add a Trigger
- To add a trigger to a file use
command ADDPFTRG

- Triggers are always added to a
physical file, but trigger occurs
however record is accessed



Add a Trigger



Gotcha (i)
Need to get an exclusive lock
on a file to be able to add or
remove a trigger

Solutions:
1) Log on late at night when
nobody is using the system.



Gotcha (i)
remove a trigger

Solutions:
2) Give up!



Gotcha (i)
remove a trigger

Solutions:
3) Write a little application to perform
the add remove triggers
a) Create a file with add/remove
flag and all the attributes for the
command


Gotcha (i)
remove a trigger

Solutions:
3) Write a little application to perform
the add remove triggers
b) write a program that runs at an
appropriate time that reads this
file, performs actions and deletes


Gotcha (ii)
Once a job has fired the trigger
the program referenced on
trigger gets locked to the job.

Solution:
Write a generic trigger program that is
called by any trigger that you ever add.
This trigger program analyses the string
passed to it by the trigger and reads a file
to decide which program to call, passing
the trigger data to it.


Gotcha (iii)
The execution of the logic
defined in the trigger becomes
part of the I/O operation
against the file.
Solutions:
If adding any long running operations
as part of a trigger make sure it
submits the job, preferably to a multi
threaded job queue.



Data
What data is passed by the
operating system to the trigger
program?

Two parameters:
1) A long string containing control
information followed by the
before and after images of the
record processes.



Data
What data is passed by the
operating system to the trigger
program?

Two parameters:
2) A 4 byte binary number containing
the length of the string passed.



Data
Trigger control information.
1-10 Name of the file being triggered
11-20 Library of the file being triggered
21-30 Member being triggered
31 Trigger event
1 = Insert 2 = Delete
3 = Update 4 = Read
32 Trigger time
1 = After
2 = Before


Data
Trigger control information.
37-40 CCSID of the file (4 byte binary)
41-44 RRN of the record being processed
(4 byte binary)
49-52 Offset to the before image of the
record (4 byte binary) (orgoffset)
53-56 Length of the before record (orglen)
57-60 Offset to the after image of the
record (newoffset)
61-64 Length of the after record (newlen)


Data
To extract the before image in
RPG:-
Eval orgrecord=%subst(buffer:orgoffset:orglen)
Eval newrecord=%subst(buffer:newoffset:newlen)



Generic program
The last thing the generic program needs
to do is access the file you have created
to decide which program to call.

For instance this file would tell the
generic program that when a record
is add to file CUSTOMER in library
SHOWMEDEMO that it should call the
relevant program


Generic program
Recommend that all is a generic program
and then pass to each individual routine

1) The current user (Defined in
the program status data area
of the generic program



Generic program

2) The trigger event (Insert,
Update, etc.)
3) The trigger time (Before or
After)



Generic program

4) The before image
5) The after image



Generic program
In the called program defined two data structures:-

d b_recordstr e ds extname(CUSTOMER) prefix(b_)
d a_recordstr e ds extname(CUSTOMER) prefix(a_)

Then move the before image into structure b_recordstr
move the after image into structure a_recordstr



Generic program
You now have all fields from the before image available
to the program, for example:

B_BALANCE
B_NUMORDS



Generic program
And all the fields from the after image, for example:

A_BALANCE
A_NUMORDS



Client Examples
Sending an email to
customer services when a
customer goes over their
credit limit, maybe
attaching a spreadsheet to
all their open invoices



Client Examples
Creating a workflow for
order acceptance including
order acknowledgement,
picking lists, delivery notes
and invoices



Client Examples
Creating an audit log of
any changes to fields on
required files. Can log user,
date and time, program
name, and before and after
image of any or all fields.



Client Examples
Replicate the data via an
SQL statement into other
tables or applications



Other commands
CHGPFTRG Change trigger, can change status to
*ENABLED or *DISABLED – needs
exclusive lock
RMVPFTRG Removes a trigger – needs exclusive
lock

PRTTRGPGM List all the triggers in a particular
library *ALL



Considerations

Consider writing your generic trigger
program to read a file of triggers to
ignore. In this way you can turn any
particular trigger off and back on without
needing to have an exclusive lock.



Happy Shooting!
Keep your trigger finger handy! Should
you wish to learn more on how we helped
businesses with their automation
requirements please contact me.

sclose@uti400.com
www.uti400.com


Questions and Answers

Steve Close
Utilities 400 Limited.

Utilities 400 NiSUG Trigger Presentation

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