On Wed, May 19, 2010 at 1:12 AM, ak37 <rendy.anth...@gmail.com> wrote:
> I just tried the new Model Validation feature in Django 1.2 and I
> found out that ModelForm always calls the Model's clean method even
> when the form validation has errors. This causes problems when the
> model has a foreign key, and the value is validated in the clean
> method. Consider this example:
>
> class Flight(models.Model):
> aircraft = models.ForeignKey(Aircraft)
> departure = models.ForeignKey(Departure)
> arrival = models.ForeignKey(Arrival)
>
> def clean(self):
> # There can never be flights departing and arriving to the
> same place
> if self.departure == self.arrival:
> raise ValidationError("Departure is the same as Arrival")
>
> class FligthForm(forms.ModelForm):
> class Meta:
> model = Flight
>
> If the form is submitted with empty values, I will get a DoesNotExist
> exception when trying to access the self.departure/self.arrival
> attribute in the clean method. Is this by design? If it is then what
> is the recommended practice to implement the Model's clean method?
>
Calling the model clean() even though validation errors have already been
noted is consistent with the way form validation is done: the form-wide
clean() is called even when validation errors have been raised for
individual fields. It's up to the form-wide clean() to make sure the values
it wants to work with survived the earlier cleaning attempts; this is noted
for example here:
http://docs.djangoproject.com/en/dev/ref/forms/validation/#cleaning-and-validating-fields-that-depend-on-each-other.
Similarly a model clean() method must be aware that the values it has may
not be valid per earlier validation that has been run.
In this specific case one way to deal with the issue would be to use a
try/except block and catch the DoesNotExist. If one is raised, you may
assume that that error has already been noted by the form cleaning, and just
ignore it.
(I am a little confused by your model definition though -- you have
departure and arrival defined as ForeignKeys to different models, so I don't
see how they would ever compare as equal, unless your actual code is
checking some attribute on each rather then equality of the foreign key
values themselves?)
Karen
--
http://tracey.org/kmt/
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