> Betreff: Re: [Zope-dev] z3c.form - extraction from sequence widget
> Hi Roger,
> >> Btw., it is possible to have a three-state widget for
> booleans, such
> >> as a drop-down widget, that includes "True/False/None",
> although it
> >> may not make much sense.
> > No that's not possible! Because you can't save anything
> then False or
> > True in a Bool field.
I was a little bit unclear. I meant that the widget can't
save back None as a new value after True/False was set.
> Really? How is this different to having a not-required Int,
> Float, TextLine or whatever field, with no default? Do they
> then semantically default to 0, 0.0, "" etc, or are they
> expected to be None? My assumption is that they're None when
> not explicitly set.
Yes, you are right the default is set to None
like any other field which doesn't define something else.
The problem is, if you use a widget and the widget
uses None as an option e.g. True/False/None for
act as (True, False and not set) then the field
validation whould not allow to set anything then
True or False as a value.
The initial value could be None, but after set to
True or False this initial (None) state can't get
set again. That's sometimes useful but sometime not.
> > I think it's always bad idea to use default=None for Bool fields.
> > Because of it's invalid defaults.
> I guess that depends on whether you think "not set" means
> "invalid". In SQL, for example, any field type can accept
> NULL (unless the column is defined NOT NULL).
I see your point, None is often use as an indicator
for a not set value. I'm not so sure if this is a good
concept for any use case. I use that concept too im my
projects for Bool fields. But I also use some Choice
fields with explicit (True/False/None) values for allow
to reset a already set value.
What I tried to say is: None is a possible inital value
but this value is invalid for Bool fields. If the goal
is to indicate a *not set value* then we are fine. If you
set the field to require=True and that's fundamental part
of your business logic, then it could end in a nightmare
because of the invalid default. At least if the application
will access the field value before someone changed that
to a valid value.
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