Bare "except" dangerous to ZODB? was Re: [Zope-dev] Accept-Charset hearders causing 500 internal server error.[correct but not lenient]

[Shane Hathaway]

Toby Dickenson wrote:
> On Monday 10 February 2003 8:47 pm, Shane Hathaway wrote:
> 
> 
>>>Great, so there's at least 133 things to examine to see if they
>>>could catch a ConflictError.  And I only wrote about 15 of those.
>>>The rest could be very time-consuming to audit.
>>
>>"tal:on-error" also catches all exceptions.  It could be made to catch
>>all exceptions except ConflictError, but I don't feel like that's the
>>right solution. 
> 
> 
> A while ago I tracked down a bug in one of our products to a case where a 
> mutator method failed half way. It raised an exception and left the object in 
> an invalid state. This would be safe except for a dtml-try that swallowed the 
> exception. 
> 
> Recently I have been experimenting with this attached module to ensure that an 
> application-level object can veto a transaction. I guess it would be 
> applicable to ConflicctErrors too.

Ah-ha, that's a very elegant approach.  By reusing the notional 
"transaction participant" interface, you didn't have to change the 
behavior of transactions in any way.  Cool.  We should definitely do it 
that way.

I'm thinking the veto should be added by Connection.commit() and 
Connection.setstate() whenever a conflict is about to propagate.  What 
do you think?

Shane