One thing I'm pretty sure of is that my manager probably think I spend
to much time on this :).
If you change a field from length of 20 to 50, I don't see how you can
just update the DB layer service program and call it the day. Are you
going to just assume that all existing programs that use the getter
method would work just fine even though the receiving variable is still
declare as 20 in length?
. . .
If you have the following type of DB getter:
D getMyFileNextRec pr likerec(MYFILEFmt)
Or
D getMyFileNextRec pr N
D piResultDs likerec(myFILEFMT)
Without recompile the caller that uses above type of getter method might
result in corrupt data.
. . .
There is a big different between RPG's chain/read.. and your own
getMyFileNextRec(). Chain/read normally does not share access path
between program (Unless specifically override by program). Your own
getMyFileNextRec() is global (Unless implement special code to prevent
it. Not going to be easy). For example if program A has a Dow
getMyFileNextRec() and within the do loop it calls program B. If
program B happens to execute getMyFileNextRec(), the Do loop in program
A is likely to get mess up.
-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Joel Cochran
Sent: Tuesday, October 02, 2007 3:13 PM
To: RPG programming on the AS400 / iSeries
Subject: Re: MVC in RPG?
On 10/2/07, Lim Hock-Chai <Lim.Hock-Chai@xxxxxxxxxxxxxxx> wrote:
3. If you still have to do research on all programs that uses the DB
layer when changing attribute of a field, you are really not gain much
from it. As far as adding new field, it is only true if your DB layer
does not have procedure that allowed caller to get the entire DS of
the file. Unfortunately, getting the entire DS is a pretty useful
function to have.
OK, let's look at this another way. Using "Classic I/O", you would have
to find all the code that references the field anyway, so you aren't
losing anything there.
With the database layer, you have the option of updating the consuming
code, but it isn't required: you could leave the original procedure
intact, so that preexisting code continues to function, and add a new
procedure for the updated length of the field. You could even change
the code of the original procedure to call the new one behind the
scenes, making whatever adjustments are necessary to make the two
compatible.
If you need to add data integrity checking, you only add it ONE TIME to
the database layer. Let's say the business rules for a field change,
whether the field definition changes or not: in option A, implementing
that business rule requires you to find every instance in your code that
references that field, updating the behavior, and then recompiling all
the *MODULES, and updating or recompiling all the programs. In option
B, using a database access layer requires changes to only one code
source: it gets compiled, and an UPDSRVPGM command is issued.
From a maintenance standpoint, I like option B a lot better. And
honestly,
how often are you changing the attributes of existing fields?
As for the DS issue, I'm not sure I follow: retrieving the DS from the
Service Program would simply return whatever the current definition is.
If your code does not consume new fields, then what is the issue?
4. There are several ways to go around the problem, the point being
that are you really gaining anything from DB layer? Why replace RPG
io functions that all RPG developers are familiar with with your own
io functions that no new comer can understand without additional
trainings?
The functions are no more difficult than any other call to any other ILE
procedure. And you aren't REplacing the IO functions, you are
DISplacing them. I wouldn't hire a programmer who couldn't grasp this
quickly. If anything, you are making their job easier because they only
need to knwothe interface, not the entire database. It is definitely
not rocket science.
--
Joel Cochran
http://www.developingfor.net
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