[Zope3-dev] Proposal: Vocabulary Fields

[Steve Alexander]

Martijn wrote:
>>> I still disagree with this multiplication of entities; we now have 
>>> fields and enumerated fields while before we just had one kind.
>>> I still haven't seen a motivation for this.


Guido wrote:
>> Isn't there a way to make the "enumerated" part an option, like
>> min_size and required, rather than a new type?

Steve wrote:
> Yes.
> 
> I explained this in my earlier email to this list and to Fred.
> 
> I'll try to dig out the reference from the archives.

http://mail.zope.org/pipermail/zope3-checkins/2003-April/008335.html

So, it wasn't this list.

Here's the relevant part:


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(SteveA)
I was going to make a similar change to this field type.
However, rather than make a different implementation class, I was going
to use the same implementation class, and have instances change their
own interface declaration depending on whether allowed_values is defined.

This allows you to use a different widget for an any-values fields to
the one used for an allowed-values field.

Other than this change of constraint, I see no problem with the same
implementation being used. I see no more problem with changing an
allowed_values constraint on a Field instance than with changing any
other constraint on a Field instance.

(Quote from Fred)
 > As I'm sure you understand, the biggest aspect of schema change is
 > proper support for the new schema in the application, and when
 > expanding the set of allowed values for a field, the hardest part is
 > ensuring the code has been tested thoroughly and that edge cases are
 > properly located and checked.  There's far more than making a couple
 > of edits to spelling of the schema.

(SteveA)
Do you propose disallowing any other changes to the notional set of
valid values for a field?

Do you want Field instances to be immutable?

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-- 
Steve Alexander