[Zope] Session set/read in same request

[Chris McDonough]

Zope sessioning data is transactional.  You are setting a session
variable in one database connection, and presumably before the
transaction that involves that connection has a chance to commit, you
are telling the browser to redirect, which has the behavior of opening a
separate connection which may or may not see the changes committed by
the first connection to the database.  This is actually a race
condition.  It might even work sometimes but it's dependent on outside
factors.

Arguably, there's no good reason to use __bobo_traverse__ unless you're
trying to make non-ZODB objects appear as if they were traversable (it
doesnt appear from your example that you're doing that).  Ditch
__bobo_traverse__ and move the send-this-guy-to-a-different-page logic
into a script or template.  And then instead of redirecting to the
content object in the if response == "1" stanza, "return
content_object.script_or_template_name()", which should then do the
right thing.

BTW, I fully expect you to say that this won't work for you.  I can
sympathize but going down the road of telling the initial connection to
commit explicitly is possible but fraught with peril.  It's so perilous
that I need to refuse on moral grounds to even explain how to do it! ;-)

- C


On Mon, 2004-09-13 at 14:00, Dan Fairs wrote:
> Hi,
> 
> I'm trying to set and then read a session variable on the same request.
> Basically, I have a script which sets a session variable when called, and
> then redirects back to a content item. That item's __bobo_traverse__ then
> looks for this variable.
> 
> Trouble is, the variable I'm setting doesn't seem to be present when I
> check it.
> 
> My 'setter' script looks like this:
> 
> if response == '1':
>     context.REQUEST.SESSION['secure_acknowledge'] = 1
>     context.REQUEST.RESPONSE.redirect(site.absolute_url())
> 
> The relevant lines in the site __bobo_traverse__ are:
> response = self.REQUEST.RESPONSE
> if not self.REQUEST.SESSION.has_key('secure_acknowledge'):
>   zLOG.LOG(__name__, 0, "no ack")
>   cr = self.portal_url.getPortalObject()[CONTENT_ROOT_NAME]
>   response.redirect(cr.absolute_url() + '/secure_site_notice?came_from=%s'
> % self.UID())
> else:
>   zLOG.LOG(__name__, 0, "ack")
> 
> ... I always end up with 'no ack' in my log.
> 
> If I dump the contents of the SESSION just after the variable is set, then
> I can see it - but it's gone by the time I actually want to process it!
> 
> What am I doing wrong?
> 
> Cheers,
> Dan
> 
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