On Tue, 2007-05-22 at 08:11 +1000, Malcolm Tredinnick wrote:
> On Mon, 2007-05-21 at 14:00 -0500, Tim Chase wrote:
> > > What is the "general way" to add your own validation to forms under
> > > the newforms framework?
> > >
> > > Subclassing and adding in your clean_* methods? Using decorators or
> > > the such around existing validation? Adding your own custom Field
> > > objects and setting their "clean" methods?
> >
> > My understanding (easily wrong, and appreciating correction if
> > so) is that they are divergent concepts, each of which serves its
> > own purpose.
> [...]
>
> > Perhaps
> > one of the framework gurus could shed light on "the way it should
> > be done"...
>
> Tim's explanation is mostly on the money. Since I have a "framework
> guru" T-shirt around here somewhere (actually, I don't -- I want to get
> a Django T-shirt one day), here's my understanding.
>
> There are three types of cleaning methods that are run during form
> processing. These are all executed when you access Form.errors or call
> call Form.full_clean() explicitly (or Form.is_valid(), which accesses
> Form.errors).
>
> Any cleaning method can raise ValidationError if there is a problem with
> the data it is processing, passing the relevant error message to the
> ValidationError's constructor. If no ValidationError is raised, the
> method should return a Python object for the cleaned (normalised) data.
>
> The three types of methods are:
>
> (1) The clean() method on a Field subclass. This is responsible
> for cleaning the data in a way that is generic for that type of
> field. For example, a FloatField will turn the data into a
> Python float or raise a ValidationError.
>
> (2) The clean_fieldname() method -- where "fieldname" is
> replaced with the name of the form field attribute. This method
> does any cleaning that is specific to that particular attribute,
> unrelated to the type of field that it is. In Matt's original
> problem, clean_username() would be the right place to do any
> uniqueness validation. You don't need a specific Username field
> -- it's just a CharField, really -- but you want a
> formfield-specific piece of validation and, possibly, cleaning.
Something I should have made clear, here (I think the people replying to
this thread already understand this, but I'm trying to be
comprehensive):
The clean_<fieldname> method is a method on your Form subclass, not on
any particular field. So you would write a form that looks like:
class MyForm(forms.Forms):
username = forms.CharField(...)
def clean_username(self):
....
return nice_shiny_clean_username_string
Regards,
Malcolm
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