[Zope-dev] Re: [ZCM] [ZC] 869/ 5 Comment "Broken transaction handling in case of exceptions"

[Toby Dickenson]

> The view has access to the original request that ended in the error. The
> view is looked-up and rendered in a new transaction.

A new transaction means that *arbitrary* changes may have occurred to the 
application state in between:
1. the transaction that raise the error, and
2. the transaction that reports it

In principal it is posssible to delete the database state and import a whole 
new application between these two points. The object containing the 
originally published method might no longer exist. I guess that might not 
matter if your error page just says "sorry an internal error has occurred" - 
if you want your users to be shielded from the details of any problem. I have 
some applications at the other extreme, where the users are all capable of 
debugging any problem and I want the error page to be a "core dump" of 
application state. 

> Can you give an example of the kind of situation where you'd need access
> to objects in a doomed transaction in their doomed state, in order to
> make an error report?

Access to the doomed state at the end of the transaction is what zope 2 gives 
us today. Access to the objects restored to their state as they were at the 
beginning of the failing transaction would be ok too (maybe even better) but 
zodb cant do that today. Either of these two are necessary for easily 
providing an error report that displays application state explaining why the 
error occurred. 


Under the Zope 3 model I think I would need to take a non-persistent copy of 
the application state in an exception handler towards the end of the first 
transaction. The second, error-reporting transaction would dump the copy, 
rather than dump what it sees to be the current world state. 

It is important that the objects passed from one transaction to the next are 
non-persistent, otherwise bad zodb-level things can happen. Does Zope 3 guard 
against this? 

-- 
Toby Dickenson
http://www.geminidataloggers.com/people/tdickenson