On Thu, 2007-10-04 at 07:37 -0700, James Mulholland wrote:
> Hi,
>
> [Note: apologies for the double post. Google didn't offer to preview
> the message, which is what I was trying to do...]
>
> I'm starting to investigate newforms in detail (having previously used
> the old forms library) since I have a job to convert an Access DB to
> web format. The client wants to maintain a similar layout to what they
> have in Access, which in places means having one page which has
> several records on it. To test out some ideas, I've made a simple app
> which attempts to edit two database records from the same web page.
>
> models.py
>
> class Country(models.Model):
> name = models.CharField(maxlength=100)
> iso = models.CharField(maxlength=2)
>
> class Address(models.Model):
> address_1 = models.CharField(maxlength=60)
> address_2 = models.CharField(maxlength=60, null=True, blank=True)
> town = models.CharField(maxlength=30)
> county = models.CharField(maxlength=40)
> country = models.ForeignKey(Country)
>
>
> views.py
>
> def edit_address(request, id=None):
> address = Address.objects.get(pk=id)
> country = address.country
>
> AddressForm = form_for_instance(address, fields=('address_1',
> 'address_2', 'town', 'county'))
> CountryForm = form_for_instance(country, fields=('iso', 'name'))
>
> class FullForm(forms.Form, AddressForm, CountryForm):
> pass
This is the problem line. You are hoping for behaviour from multiple
inheritance works in Python that isn't valid. Firstly, there would be
some problems here because the save() method will only call the save()
method on one of the subclasses, not all of them. Probably other
unintended side-effects as well.
Instead of trying to create a mega-form like this, just work with the
two forms independently. You can initialise a form using a data
dictionary (request.POST in this case) that contains more information
than is required for the form. The form class will only use the fields
it requires.
So after creating AddressForm and CountryForm, the continue with:
address_form = AddressForm(request.POST)
country_from = CountryForm(request.POST)
and so forth. You can happily pass both forms to the template for
rendering and everything like that.
Alternatively, if you truly do want only a single form class, you can
write your own variation on form_for_instance that takes multiple
instances from different classes and does whatever you expect. I would
expect that just using two form classes will generally lead to more
readable code, though, unless you are doing this a lot with lots of
classes on a page (in which case I'd write the helper function).
Regards,
Malcolm
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