RE: CHAIN or READ without lock

["John Taylor" <john.taylor@xxxxxxxxxxxxxxx>]

> -----Original Message-----
> From: owner-rpg400-l@midrange.com [mailto:owner-rpg400-l@midrange.com]On
> Behalf Of fkolmann@revlon.com.au
> Sent: Thursday, February 10, 2000 9:35 PM
> To: RPG400-L@midrange.com
> Subject: CHAIN or READ without lock
>
>
> Thought I would check if others have experience something like this.
>
> The CHAIN or READ without lock is a new function (well sort of) , but do
> you know it also READS LOCKED records.
>
> We had duplicate invoice numbers in our order processing application.
> It was caused by  the 'N'  (no lock ) on a CHAIN op.
> I checked the manual and if you read the fine print, yes  you can read a
> LOCKED record with
> a CHAIN or READ  even if the file is opened for UPDATE, provided you use
> a N to request a
> read without lock.
> Personally I stay away from the read without lock.


This is exactly how I would expect it to work. If this behaviour is what is
causing your duplicate invoice numbers, then I respectfully suggest that you
re-think your application design.

One common method of obtaining unique invoice numbers would be as follows:

FILEA - Tailoring file that stores the next available invoice number.
FILEB - Invoice Master

1) Chain to FILEA with a record lock.
2) Retrieve next available invoice number.
3) Chain to FILEB without a record lock to test for duplicate invoice
number.
4) If duplicate found, increment next available invoice number & repeat.
5) Once you have a unique invoice#, write invoice header record to FILEB.
6) Increment next available invoice number.
7) Commit changes.

Of course, standard error handling is required for lock timeouts, invoice#
rollover etc.


Regards,

John Taylor
Canada

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