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

[ender]

On Tuesday 27 March 2001 17:40, Itai Tavor wrote:
>>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)?

check out dtml-contract.

sample form processor with dtml contract

<dtml-contract>
this page retrieves records from the db based on user input
<dtml-params>
foo:int,optional
bar:date
foobar:range(int, 0,10)
<dtml-exceptions>
bad_user_input
</dtml-contract>

user gets redirected if bar is not a valid date string, and foobar is not a 
integer compatible string between 0 and 10. if foo is present it must be a 
integer compatible string (compatible means coercible via int(foo)). if any 
of these things does not happen than all the collected errors for the page 
are sent to the error handler bad_user_input. this is not a redirect, the 
error handler is evaluated in the context of the page with an additonal value 
added to the namespace to denote the list of errors. page processing stops 
after evaluation of the tag if an error occurs.

this may be clear as mud, i don't know, i tried to make the included 
documentation pretty inclusive and readable, its not completely insync with 
the code but it does elaborate on the feature set pretty well. if you have 
specific questions feel free to ask.

so in your case you can just use the original form as the error handler and 
add logic to it to insert the values if they already exist in the request, 
and display error messages to the user on the particular vars that have 
problems based on the existence of the special error variable.

hth

kapil


>>TIA, Itai