[Zope-dev] ZPatterns, DataSkins, forms and error checking/handling

[Itai Tavor]

Hi,

I'm trying to work out the best way to check for and report errors 
when DataSkin objects are created/edited, but I'm having a lot of 
problems.

For form validation, Zope's build-in constraints are pretty 
useless... things like ValueHandler are a little better, but IMO not 
good enough. When a user types incorrect data in a form, I don't want 
to display a page with a list of errors and say "click Back to fix 
your errors". I want to return the form, with a list of errors and 
the bad fields highlighted. So I need to perform field checks in the 
form action method and in case of errors call the original form, 
giving it an error list.

I know that to ensure that object data is always valid I should 
validate the object in a SkinScript, using WHEN OBJECT ADDED,CHANGED 
call self.validate(), and raise an exception in validate in case of a 
problem. But this can't deal with returning the original form. It can 
only display error pages, and to display nicely formatted error pages 
it has to return a DTML Method so I can use dtml-raise, rather than 
directly do raise in validate.

So I'm looking at a validate method for use at commit time, a 
show_errors DTML Method, and a validate_form to call from the form 
action method...

The validate_form method is defined in the DataSkin class. But it is 
also used when a new object is created from a form, so it needs to be 
called from a Specialist before the object is created, so I need to 
import it in the Specialist. But this method might use other methods 
of the DataSkin class, so I need to import those too...

So, to sum up, I need a method used in commit time, that renders a 
DTML method to raise an error message, another method to verify form 
submissions and return the form with error messages, and I need to 
import that method and all other methods it uses into the Specialist. 
This seems too much work...

Can anyone suggest a simpler approach (one that still retains the 
ability to return the original form in case of errors)?

TIA, Itai
-- 
--
Itai Tavor                      -- "Je sautille, donc je suis."    --
itai@optusnet.com.au            --               - Kermit the Frog --
--                                                                 --
-- "If you haven't got your health, you haven't got anything"      --