Django form validation making required conditional

Question

I'm new to Django (and Python), and am trying to figure out how to conditionalize certain aspects of form validation. In this case, there's a HTML interface to the application where the user can choose a date and a time from widgets. The clean method on the form object takes the values of the time and date fields and turns them back into a datetime.

In addition to the HTML interface, there's also an iPhone client making calls into the application, and I'd like to pass a UNIX timestamp-style time value in.

My form code looks like this:

class FooForm(forms.ModelForm):
    foo_date             = forms.CharField(required=True, widget=forms.RadioSelect(choices=DATE_CHOICES))
    foo_time             = forms.CharField(required=True, widget=SelectTimeWidget())
    foo_timestamp        = forms.CharField(required=False)

How do I make foo_date and foo_time required unless foo_timestamp is provided?

Answer 1

This is done with the clean method on the form. You need to set foo_date and foo_time to required=False, though, because clean is only called after every field has been validated (see also the documentation).

class FooForm(forms.Form)
    # your field definitions

    def clean(self):
        data = self.cleaned_data
        if data.get('foo_timestamp', None) or (data.get('foo_date', None) and data.get('foo_time', None)):
            return data
        else:
            raise forms.ValidationError('Provide either a date and time or a timestamp')