[Zope-CMF] Re: RFC: first stab at viewification

[yuppie]

Hi Tres!


Tres Seaver wrote:
> I just checked in a preliminary pass at viewifying the
> 'full_metadata_form' (now 'metadata.html' as a view):
> 
>   svn+ssh://svn.zope.org/repos/main/CMF/branches/tseaver-viewification
> 
> A couple of things to note:
> 
>   - I adopted a "don't generalize too soon" approach on this,
>     rather than trying to come up with a perfect reuse example.
>     I have two views registered, 'metadata.html' for the template
>     and 'metadata.py' for the controller to which it POSTs (since
>     it needs to do redirects).  This is a sort of "hybrid" strategy.

Before discussing *how* to implement the 'form flow' we should try to 
agree on *what* we want to implement.

The best 'form flow' pattern I know (for browser forms, without using 
tokens or sessions) is this:

- Forms should always be POSTed to themselves. This is the only way to 
keep the URL consistent if we response with validation error feedback. 
Redirecting to the original location is no option because we can't get 
the POST data through a redirect.

- If a form submission was successful (means triggered a database 
change), the response should always be a redirect. See this link 
(Post/Redirect/Get pattern) for the reasons: 
<http://www.theserverside.com/patterns/thread.tss?thread_id=20936>

CMFFormController uses that pattern and most CMF 1.5 forms follow that 
pattern.

Your "hybrid" strategy works only if you *always* redirect. So it is not 
suitable for implementing that pattern. Your example has no validation 
and ignores completely the possibility that 'update' might fail.

> I need to review Yuppie's branch for folder_contents as well:
> 
>   svn+ssh://svn.zope.org/repos/main/CMF/branches/goldegg-folder_contents

This branch is work in progress.

What it does already:

- It shows how to use the __call__ method as dispatcher. I still believe 
that using the __call__ method for this is the Right Thing.

- It splits up the big folder_contents script in a set of small methods. 
I came quite far, but I'm not done.

- It doesn't change any behavior or functionality of folder_contents.

- It shares the template with the skin. This is just a proof of concept, 
not sure if we need that.

What's still missing:

- Only folder_contents itself is converted into a view. It still depends 
on several skin scripts.

- There are no unit tests.

- Some methods are called more than once. Some kind of caching might be 
useful if these methods perform expensive tasks. The most expensive 
tasks are currently performed in the __call__ method to make sure they 
are called only once. I'm not happy with that.

> Feedback on both branches would be appreciated;  we have folks gathering
> here in FXBG to hammer out the remaining viewification plan for CMF 2.0
> next week.

metadata.html/metadata.py has some issues that are not related to the 
viewification itself, but are new compared to full_metadata_edit:

- In CMF 1.5 all method names (besides folder_contents) are fully 
configurable through Actions and Method Aliases. metadata.html has 
hardcoded method names.

- metadata.py doesn't catch ResourceLockedErrors.

- The controller code is not scalable. Adding validators doesn't look 
very easy and implementing something like folder_contents looks almost 
impossible.


Cheers,

	Yuppie