why not query the database first to see whether the chosen name
already exists? That's what i do in a validator function for a deform
form. Other than the potentially superfluous database query I see no
downside to this.
regards
robert

On Thu, Oct 27, 2011 at 2:51 PM, Mark Erbaugh <[email protected]> wrote:
> I'm developing a Pyramid app with SQLAlchemy.
>
> I have a user registration page where user picks their user name and enter 
> other user-related information. The user name is the primary key in the 
> corresponding table. If the user picks a user name that is already in use by 
> another user, I need to inform the user of the fact and ask them to pick a 
> different user name. Pyramid apparently does an automatic commit of any 
> changes the the DBSession at the end of processing a page. When the record 
> with the duplicate primary key is inserted, SQLAlchemy raises an 
> IntegrityError exception as expected.
>
> My question is should I manually commit the DBsession inside a try ... except 
> block to catch and handle the exception in my page processing code, or should 
> I let the automatic commit fail and somehow trap the exception and process it 
> somewhere else, and if so, how and where do I trap the exception?
>
> Thanks,
> Mark
>
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