[Zope3-Users] zope.viewlet and zope.contentprovider - options for Zope 2 and Plone 3

[Martin Aspeli]

Hi guys (sorry for the crosspost, this is rather a cross-area post),

I'm reading the docs for zope.contentprovider and zope.viewlet, and there  
are many reasons why we'd like to use this in Plone. The way the release  
cycles work, Plone 3.0 would be the natural place to put some of this.  
Now, I have a few questions:

  - In what version of Zope 3 did zope.contentprovider and zope.viewlet  
appear? They're not in my Zope 2.9 lib/python/zope.

  - Are they scheduled to be in Zope 2.10?

The main achilles heel as far as I can tell is the TALES 'provider:'  
expression. I'm guessing that without using the Zope 3 ZPT and TALES  
implementations, Zope 2 won't be able to use these.

  - Is it the intention to use the Zope 3 ZPT and TALES engines in Zope  
2.10? If not, are they scheduled for some other time? How much work is  
needed for this to be a reality?

Now, I have a feeling that this could be faked in Zope 2 with something  
like:

	<tal:block replace="structure python:provider('provider.name')" />

the object 'provider' would have to be defined globally (in  
global_defines.pt in Plone). Its implementation would basically be  
identical to the TALESProviderExpression in zope.contentprovider, with a  
__call__() method that called update() and render() on an IContentProvider  
looked up by the name it was passed.

The tricky part is the ITALNamespaceData update magic that needs to read  
the TAL context:

  - Is there some way a python object referred in an expression like the  
one above could be passed or acquire (literally or figuratively) TAL  
objects defined in the current context at that point?

  - If not, based on your practical experience, how much is this used -  
would zope.contentprovider and zope.viewlet be useless if Plone had to say  
"we only support a subset of the zope.contentprovider API" (note: we  
really don't want to do that, I'm just looking at options here)

The other problem with this implementation is that it would call  
viewlets/content providers sequentially, i.e. call update(), then render()  
for each object as it discovered them, not call all the update()'s and  
then all the render()'s. I note that the zope.contentprovider README.txt  
mentions that this is bad, but the TALESProviderExpression implementation  
seems to suffer from exactly the same problem.

  - Is this expected behaviour? Is it considered as "known issue"? Are  
there plans to improve on this?

Thanks a lot!

Martin



-- 
(muted)