[Zope3-dev] Re: Field binding considered icky

[Garrett Smith]

Jim Fulton wrote:

> I'm trying to catch up a bit on documentation.  I'm working on
> README.txt files for zope.interface and zope.component and will be
> updating the README.txt for zope.schema.
> 
> There is a "feature" of schema fields that I really don't want to
> document.   This feature is called "binding".  A field can be "bound"
> to an object.  This creates a new field instance, which is a clone of
> the original, that has a `context` attribute which is some object.
> The object *may*, for example, be an object that has an attribute that
> is specified by the field.

Apart from being hackish (er...icky?), why does the current approach 
need to be revamped?

>    We would get rid of the validate method of fields.
> 
>    When we want to validate a field, we'll adapt it *with* it's
>    context:
> 
>      >>> validator = getMultiAdapter((field, context), IValidator)
>      >>> validator.validate(value)
> 
>    A disadvantage of this approach is that it will require either
>    that:
> 
>    - We remove validation logic from zope.schema, or

This doesn't seem like a disadvantage.

>    - Introduce a dependency of zope.schema on zope.component.  Later,
>      if we merge zope.schema into zope.interface, we'd introduce a
>      dependency of zope.interface on zope.component.

This definitely seems like a distadvantage.

> B. Widgets
> 
>    Widgets would become multi-views:
> 
>      >>> widget = getMultiView((field, context), '', request, IInputWidget)

This makes sense.

> B'. Rather than using multi-views, use views of multi-adapters:
> 
>     >>> widget = getViewProviding(
>     ...             getMultiAdapter((field, context), someinterface),
>     ...             request, IInputWidget,
>     ...             )
> 
>     The idea is that the widget need not know about context. Any knowledge
>     of the context is restricted to the adapter.  I think that this
>     has some appeal, but I don't know that I want to require it.

This is getting a bit crazy :-)

>     I don't like this option

Same here.

> Thoughts?

In the current implementation, we get to context as an attribute of the 
bound field. Is the primary motivation for using multiadapters and 
multiviews to avoid the field cloning?

  -- Garrett