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Kurt,
Can you tell me why you think file encapsulation is worth the effort? I
spent many years thinking on this, and found that I don't like the
bottom-up mindset that this imposes on application development.
I find my development patterns seem to take a top-down approach, defining
business "objects" or entities, and methods (business transactions) to
process these entities, and invoke whatever file I/O approach that best
serves the needs of the transaction.
At issue, to me, is that the file encapsulation limits you to a handful of
methods to retrieve your data, and limit your flexibility as a developer.
Say for example that I only need a subset of fields from a particular
file. Unless I specifically define a proc to return just the fields I
want, the standard mode of operation is to simply return all the fields in
the file.
Instead of designing on top of the database, design the functions that
support the meta-data contained within the database. In CUST file, you
might have a data function to retrieve billing or shipping address, another
for YTD summary details, another for A/R credit terms, and so forth...
JMO,
-Eric DeLong
-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx]
On Behalf Of Kurt Anderson
Sent: Tuesday, April 03, 2012 4:35 PM
To: RPG programming on the IBM i / System i (rpg400-l@xxxxxxxxxxxx)
Subject: File Encapsulation Quandary
Being a big fan of file encapsulation (essentially centralizing business
logic relating to a file), I've created a fair number of file encapsulated
service programs. They use native I/O. Since the service program is a
one-stop shop, the file is defined as Update/Add. This causes a couple
issues:
1. File needs to be copied into a test library.
In our environment we don't have separate test and production
environments. In fact, most testing references a client's production
library. This has actually worked fine without consequence. We always
run STRDBG UPDPROD(*NO) for testing. What this means is that any file that
is encapsulated needs to be copied into a test library otherwise the
service program won't open the file. This is a minor pain (however has on
occasion caused issues in testing b/c a file had pre-existed in a test
library and it wasn't updated).
2. Files opened for update don't block read.
One of our main files I really wanted encapsulated couldn't be because
it's a transaction file with millions of records. No blocking on read
loops hurts. A lot.
3. Using SQL bloats job log in test mode. Slows single-record access.
IBM has really been pushing using SQL to access data, so I thought this
might be a good occasion to follow that path they've laid out. Doing so
addresses issues #1 & #2 above. I've modified one of our file encapsulated
service programs to use SQL. I think it works pretty slick. Although one
not-so-slick aspect is the "chain." Presumably Closing an existing cursor,
Preparing a cursor, Declaring the cursor, then Fetching the cursor is going
to be a lot slower than a simple chain. I'm willing to live with that,
although I'm getting some beef about over-complicating it. In addition,
using SQL and running the program with STRDBG UPDPROD(*NO) balloons the job
log. Maybe I shouldn't care about the size of the job log in test,
although in one of my tests of 100,000 records (~80k chains), the job
wrapped twice and then I killed it. In this situation I may be able to
load the file into an array or something, but I know that won't always be
the case. (I do realize this is only
an issue in testing, but I can also foresee concerns about this slowing
down testing since it's writing out to the job log so much.)
This had me wondering how other shops handle file encapsulation. I know
my last job had a completely separate test environment. That's not likely
going to happen here anytime soon.
We also don't have change management software. Files being encapsulated
had made some of our file changes quite a bit easier.
Here is a sample of the code. If you have the time, I'd appreciate
comments.
http://code.midrange.com/f5aa843519.html
Thanks,
Kurt Anderson
Sr. Programmer/Analyst
CustomCall Data Systems
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