[zope2-tracker] [Bug 787541] Re: WSGIPublisher leaves the request open on error

[Brian Sutherland]

On Sun, Oct 16, 2011 at 02:51:16PM -0000, stephan_hofmockel wrote:
> Hello,
> the current implementation of this bugfix breaks the following code. 
> Assuming a request which sends 'a' and 'b' as parameters, eg. URL?a=test&b=test
> 
> import transaction
> 
> def do_something(self, request):
>     self.attribute_a = request.get('a')
>     transaction.commit()
>     ...... possible other code which raises an Exception .....
>    # the b parameter has to occur !
>    assert request.get('b') == None

There are also other situations where this code probably will not work
as expected. For example, on serialization errors Zope can retry a
request, a few times.

If you get serialization errors after commit(), it may be that the
request is retried and you get a second or third commit() where you only
wanted one.

As a bonus, serialization errors most often happen on a loaded site.
    
> I use this in situations where I would like to be sure that 'self.attrbiute_a' is inside the ZODB regardless if an error happens afterwards or not. However after transaction.commit() the request is closed, because transaction.commit() calls 'afterCompletion' of '_RequestCloserForTransaction'. This means all parameters send in a form are lost/cleared and not available anymore.
> 
> Would it make sens to change the Bugfix in ZPublisher a little bit so that
> 247         _request_closer_for_repoze_tm.add(txn, request)
>  is called after
> 252         response = _publish(request, 'Zope2')

It may help.

> If its a bug in ZOPE, I can work on a patch + test. 
> If I'm misusing transaction.commit(), plz tell me how it is done right.

I'm reasonably certain that you almost never want to call commit()
during a transaction. I've never used it, but perhaps savepoint() fits
your usecase better.

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> report.
> https://bugs.launchpad.net/bugs/787541
> 
> Title:
>   WSGIPublisher leaves the request open on error
> 
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-- 
Brian Sutherland

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Title:
  WSGIPublisher leaves the request open on error

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