[albatross-users] Random pages and application model

[Dave Cole]

> There's a nice description of how the application model relates to
> the page_xxx() methods for 'stateful' applications in the mailing
> list archive but I've not come across an equivalent explanation for
> 'random' applications.
> 
> >From debug traces I see the following sequence whenever the page is
> requested:
> 
> 	page_enter(ctx)
> 	page_process(ctx)
> 	page_display(ctx)
> 
> I have no problems with page_process() and page_display() but I
> don't quite understand what use page_enter() has? It seems a bit
> redundant to me since the request parameters are not merged into
> ctx.locals until **after** page_enter() is called.
> 
> It's probably worth explaining that what I expected to be able to do
> is something like this (not tested):
> 
> page1.py
> --------
> 
> def page_process(ctx):
>     if ctx.req_equals('edit'):
>         ctx.redirect('page2?objid=%s' % ctx.locals.objid)

Doesn't that work?

> page2.py
> --------
> 
> def page_enter(ctx):
>     ctx.locals.obj = get_obj_from_somewhere(ctx.locals.objid)

Ahhh...

In a random application the page_enter() function gets called every
request.  You could just take the page_enter() code and prepend it to
the page_process() function.

> def page_process(ctx):
>     if ctx.req_equals('submit'):
>         # save data
>         ctx.redirect('page1')
>     elif ctx.req_equals('cancel'):
>         ctx.redirect('page1')
> 
> def page_display(ctx):
>     ctx.locals.attr1 = ctx.locals.obj.attr1
>     ctx.locals.attr2 = ctx.locals.obj.attr2
>     ctx.run_template('page2.html')
> 
> 
> The problem is that, as mentioned above, the request parameter,
> objid, is not available during page_enter(), it's only there for
> page_process().

That is a bit of a bugger.  One thing you could do is subclass the
application and replace the run() method with a slightly re-ordered
sequence.

class MyApp(RandomModularSessionApp):
    def run(self, req):
        # My own processing sequence copied from
        # RandomModularApp.run() but slightly resequenced.

> One workaround is to put the object loading code in an else block in
> page_process which doesn't feel like the right place for it. The
> alternative is to transfer objid using a session var but I prefer
> not to use the session where possible - it's just something else
> that needs managing.

See if overriding the application run method gives you what you need.

The primary design goal of Albatross was to provide a toolkit from
which you can build your own application models.  We provide some
examples pre-rolled which just happen to be useful for certain classes
of application.

I am more than a little interested to see if replacing
Application.run() is useful to you.  Does it make your brain hurt, or
is it something useful?

- Dave

-- 
http://www.object-craft.com.au