[Zope] meaning error message

[Jonothan Farr]

> I see a couple of issues with this:
>
> 1)  This may not scale well; if select_data becomes large you may
> be spending a while in the dtml-in loop.

I would write the select_data query to only select a single record, i.e. the one
I'm worried about duplicating.

>
> 2)  There could still be a race condition here, between the check for
> data and the insertion (especially coupled with the above point - the
> probability would increase proportionally with the load of the machine
> and the size of the table). I say "could" here (guardedly :-), because
> I don't know how Zope's transaction semantics are implemented, and how
> they affect the DA that you're using (does anyone have any pointers to
> documents?  I've just started reading "How to Write a DA", and this
> mentions the distributed commit protocol).
>
> I'm not sure if a solution to the original problem is to surround
> the insert with a <dtml-try> tag;  I'm going to try this myself
> sometime today (if I get some spare time :-).

Good point. Yours is probably a better solution.

<dtml-try>
<dtml-call insert_data>
<dtml-except specific_exception>
<dtml-var error_message>
</dtml-try>

--jfarr