I've been thinking about how to solve this problem, and what I've come
up with so far is this:
- Schemas may be bound to a set of values. When a schema is bound,
it is cloned, and any "deferred" values it has will be resolved.
- A deferred value is a callable that accepts the schema node being
bound and a set of arbitrary keyword arguments. It should
return a value appropriate for its usage (a widget, a missing value,
a validator, etc).
- Deferred values are not resolved until the schema is bound.
- Schemas are bound via "SomeSchema().bind(**kw)". The values in "kw"
are passed to each deferred value along with the schema node being
bound.
Here's an example:
"""
@colander.deferred
def deferred_date_validator(node, **kw):
max_date = kw.get('max_date')
if max_date is None:
max_date = datetime.date.today()
return colander.Range(min=datetime.date.min, max=max_date)
@colander.deferred
def deferred_date_description(node, **kw):
max_date = kw.get('max_date')
if max_date is None:
max_date = datetime.date.today()
return 'Blog post date (no earlier than %s)' % max_date.ctime()
@colander.deferred
def deferred_date_missing(node, **kw):
default_date = kw.get('default_date')
if default_date is None:
default_date = datetime.date.today()
return default_date
@colander.deferred
def deferred_body_validator(node, **kw):
max_bodylen = kw.get('max_bodylen')
if max_bodylen is None:
max_bodylen = 1 << 18
return colander.Length(max=max_bodylen)
@colander.deferred
def deferred_body_description(node, **kw):
max_bodylen = kw.get('max_bodylen')
if max_bodylen is None:
max_bodylen = 1 << 18
return 'Blog post body (no longer than %s bytes)' % max_bodylen
@colander.deferred
def deferred_body_widget(node, **kw):
body_type = kw.get('body_type')
if body_type == 'richtext':
widget = deform.widget.RichTextWidget()
else:
widget = deform.widget.TextAreaWidget()
return widget
@colander.deferred
def deferred_category_validator(node, **kw):
categories = kw.get('categories', [])
return colander.OneOf([ x[0] for x in categories ])
@colander.deferred
def deferred_category_widget(node, **kw):
categories = kw.get('categories', [])
return deform.widget.RadioChoiceWidget(values=categories)
class BlogPostSchema(Schema):
title = SchemaNode(
colander.String(),
title = 'Title',
description = 'Blog post title',
validator = colander.Length(min=5, max=100),
widget = deform.widget.TextInputWidget(),
)
date = SchemaNode(
colander.Date(),
title = 'Date',
missing = deferred_date_missing,
description = deferred_date_description,
validator = deferred_date_validator,
widget = deform.widget.DateInputWidget(),
)
body = SchemaNode(
colander.String(),
title = 'Body',
description = deferred_body_description,
validator = deferred_body_validator,
widget = deferred_body_widget,
)
category = SchemaNode(
colander.String(),
title = 'Category',
description = 'Blog post category',
validator = deferred_category_validator,
widget = deferred_category_widget,
)
schema = BlogPostSchema().bind(
max_date = datetime.date.max,
max_bodylen = 5000,
body_type = 'richtext',
default_date = datetime.date.today(),
)
form = deform.Form(schema)
"""
This proposal does not deal with conditional inclusion or exclusion of
schema nodes, only resolving deferred schema properties.
Comments are appreciated.
- C
On Tue, 2010-09-07 at 20:37 +0800, Tim Hoffman wrote:
> Bummer ;-)
>
>
> I don't think I have a developed an application in the last 10 years
> that hasn't has to do this.
> I was quite surprised when I discovered this feature was missing in
> formish, but it seems to be missing in quite a
> few other form libs like wtforms as well.
>
> I suppose at least they all have declarative method of defining the
> schema, but it does mean the actual schema definition is a bit more
> obscured.
>
> Cheers
>
> T
>
>
>
>
> On Tue, Sep 7, 2010 at 8:20 PM, Chris McDonough <chr...@plope.com> wrote:
> > Hi Tim,
> >
> > Sorry, there is no built-in solution that will allow you to use
> > declarative-module-scope code only. You'll need to generate schemas and
> > widgets at render time.
> >
> > - C
> >
> >
> > On Tue, 2010-09-07 at 12:56 +0800, Tim Hoffman wrote:
> >> Hi Chris.
> >>
> >> Am just starting too look at deform in some detail and I have question.
> >>
> >> One of the things I have struggled with formish has been the fact I
> >> can't easily
> >> define a source of values for widgets like checkbox or validators such
> >> as OneOf to
> >> only be resolved late at render time. And I can't see how I would go
> >> about it with deform.
> >>
> >> In your example http://docs.repoze.org/deform/app.html you have
> >> colors = (('red', 'Red'), ('green', 'Green'), ('blue', 'Blue')) used
> >> as values for
> >>
> >> widget.RadioChoiceWidget values and for the validator OneOf
> >>
> >> So in my contrived example I would like the set of possible values
> >> for color is dependent on the
> >> user and some other factor. Looking at the code for SelectWidget and
> >> RadioChoice widget
> >> it appears they won't take a callable and lazily render those values
> >> at render time.
> >>
> >>
> >> With formish I basically constructed the form structure (schema)
> >> but only applied widget definitions and validators just before render
> >> time. So that I could use things
> >> like the current context to determine values for validation or
> >> choices. This was a bit of a hack.
> >>
> >>
> >> So do you have a strategy or suggestion on how to approach this use case ?
> >>
> >> I suppose I could work with imperative schema definition performed
> >> late, but I much prefer to work with classes.
> >> (I currently generate Formish (structures) directly from UML).
> >>
> >> Cheers
> >>
> >> Tim
> >> _______________________________________________
> >> Repoze-dev mailing list
> >> Repoze-dev@lists.repoze.org
> >> http://lists.repoze.org/listinfo/repoze-dev
> >>
> >
> >
> >
>
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