[Zope] q: How should I get a guaranteed unique id in Zope?

[Chris Kratz]

On Tuesday 15 January 2002 05:09 pm, Jason Earl wrote:
> I am glad that I am not the only one that has notice this "correct"
> behavior.  I especially like the fact that Zope will happily roll back
> PostgreSQL transactions on failure.  That makes combining Zope and
> PostgreSQL so much easier.

Yep, the first time it happened, I could hardly believe it.  I was looking 
through the data and couldn't find the stuff that was supposed to have been 
inserted.  The log even showed the inserts having happened, but the data just 
wasn't there.  It finally occurred to me that zope must have notified the 
database and rolled everything back when it hit the error in the dtml 
documenteven though there was no database level error.  Sure enough, there 
was a rollback buried in the log at the end of the request.  

The only caveat I have found with this behavior was again "by accident".  If 
you are in a python script or dtml and use a try-except clause to catch an 
error within zope, the rollback won't happen.  "Catching" the exception keeps 
zope from triggering the rollback machinery on the database.  One solution is 
to rethrow the exception after you have done your own processing.  We decided 
in one instance we really needed to catch the exception and we didn't want 
zope to go to the error page.  So, we created a zsql method with rollback; 
begin; in it and then use it inside of our exception code to cause the 
transaction in the database to roll back.  Now that I know more, a better 
solution probably would have been to add some logic within the standard error 
message that automatically forwarded the user to the page we wanted to end up 
on and give the user a "nice" message wthin their work environment.

Anyway, suffice it to say that 99% of the time, zope, psycopg, and postgres 
do the "right thing" which saves a lot of time.  Kudos to the respective 
authors.

-Chris

-- 
Chris Kratz
Systems Analyst/Programmer
VistaShare LLC
www.vistashare.com