[Zope3-dev] z3c.form, Object field and sub forms

[Martijn Faassen]

Hi there,

 From z3c.form's subform.txt:

"Final Note: With ``zope.formlib`` and ``zope.app.form`` people usually 
wrote complex object widgets to handle objects within forms. We never 
considered this a good way of programming, since one looses control over 
the layout too easily."

I then looked at the addressbook demo of z3c.formdemo to see how to work 
with subforms. I am somewhat intimidated, and I'm afraid others (such as 
my clients) will be a lot more intimidated. I would therefore like to 
ask the authors to consider a "bad way of programming" - widgets for the 
Object field. :)

The advantage of having a widget for the Object field to support 
complicated nested form requirements is that your code can be 
declarative. The clear disadvantage is that it's very hard to control 
the layout. This is why z3c.form argues subforms are always the way to go.

It appears however that z3c.form's subform approach also has a drawback: 
the code becomes a lot less declarative. The developer is required to 
write their own update() methods that pass control down to the subforms, 
various page templates that pass rendering control down to subforms, and 
various getContent() methods to get the correct information to modify in 
a subform.

There is a *lot* of code in the address book demo, and a lot of little 
bits which interoperate with each other. Granted, the form is 
complicated, but it's still a ton of code.

The traditional zope form approach has widgets for the Object field. The 
Object field can then refer to its own schema, and the widgets are 
clever enough to render their own subform. In combination with the List 
field very complicated nested forms can, in theory, be created with 
relatively little code.

In practice it doesn't work well, as z3c.form recognizes - it becomes 
very hard to control layout.

Wouldn't it be possible to design an Object widget where the layout *is* 
easier to control? I'm thinking about a scenario where you can easily 
supply your own subform, including template, for each Object field, if 
you so desire (there should be a default behavior). I hope that by doing 
so, some of the complicated control flow that is now in the address book 
can be eliminated.

If the addressbook demo reflects the current best way to go about 
creating a complex form, it becomes much harder for me to recommend the 
use of z3c.form. I myself need Zope 3's form system to make powerful 
nested forms not only possible, but also declarative and succinct.

Regards,

Martijn