At 02:03 PM 8/13/2004, Torsten Roehr wrote:
"Norma Ramirez" <[EMAIL PROTECTED]> wrote in message
> Thanks for answer Miles, I'm aware of what you wrote but have a little
> to find some way, and Robby what I'm trying to do is avoid the user for
> update or delete a record that other user has been already selected, so I
> cant tell something like: "This record is locked by another user, try
> later", currently I'm doing this by code but like to do by Postgres
> directly.
> Thanks in advance.

Hi Norma,

you can achieve this in a much more comfortable and elegant way:

Create an integer column named oca (stands for Optimistic Concurrency
Control Attribute). When you load the data to show them in the editing form
store the value in a hidden field or in the session (if you are using
sessions). Then when you update the data use the following statement:

UPDATE table SET column = '$value' ..., oca = oca + 1 WHERE user_id =
$user_id AND oca = $value_from_hidden_field

After performing the query check the affected rows. If there is one affected
row the update was succesful. If there are no affected rows it means that
someone else updated this row in the meantime (thereby incrementing oca) and
you can show a message like:

"Since the start of your editing process someone else updated this record
set. Please cancel and edit the record again."

This way you will never lock out a record set forever like Miles wrote and
the user will at least be able to "open" the record set and see all data -
even if sometimes (should be very seldom) he has to cancel and start again.

I hope you get my point - it's a bit difficult to explain.

Best regards, Torsten Roehr

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