Hi Martin

> -----Urspr√ľngliche Nachricht-----
> Von: zope3-users-boun...@zope.org 
> [mailto:zope3-users-boun...@zope.org] Im Auftrag von Martin Aspeli
> Gesendet: Dienstag, 7. April 2009 16:17
> An: zope3-users@zope.org
> Betreff: [Zope3-Users] z3c.form: LookupErrors
> Hi,
> In z3c.form (at least with 1.9.0), if you have a Choice field 
> and the vocabulary changes so that an existing value (or the 
> default value on an add form) is no longer valid, you get a 
> LookupError:
>    Module z3c.form.form, line 126, in updateWidgets
>    Module z3c.form.field, line 259, in update
>    Module z3c.form.browser.select, line 51, in update
>    Module z3c.form.browser.widget, line 61, in update
>    Module z3c.form.widget, line 182, in update
>    Module z3c.form.widget, line 120, in update
>    Module z3c.form.converter, line 258, in toWidgetValue
>    Module z3c.form.term, line 31, in getTerm
>    Module zope.schema.vocabulary, line 124, in getTerm
> It'd be nicer if z3c.form would catch the error and return 
> field.missing_value or something like that. As it stands, if 
> this happens with a content object, it's impossible to reach 
> the edit form and fix the value!

This is a legacy data problem. Such data need to get migrated
by a generation if a value is no longer valid.

Otherwise the wrong (not valid) value is still used in the app.
It doesn't make sense to just skip invalid values and fallback
to missing_value in the vocabulary widget since this value get
used by everthing else then the widget.

But probably if legacy data are not a problem in some apps,
we should implement a vocabulary and widget which can handle
such legacy data problems or make it a configurable option.

I also was thinking about a widget which allows to define
depreated values which are valid but not shown for selecting.
this whould allow to skip values fer a future selection.
Probably this whould require a enhanced vocabulary implementation
which offers a deprecated value list or something like that.

What do you think? Whould this fit for you?

Roger Ineichen

> Martin
> --
> Author of `Professional Plone Development`, a book for 
> developers who want to work with Plone. See 
> http://martinaspeli.net/plone-book
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