Django - How to specify which field a validation fails on?

Question

I have this model I\'m showing in the admin page:

class Dog(models.Model):
    bark_volume = models.DecimalField(...
    unladen_speed = models.DecimalField(...
         


        

Answer 1

class Dog(models.Model):
    bark_volume = models.DecimalField(...
    unladen_speed = models.DecimalField(...

    def clean(self):
        if self.bark_volume < 5:
            if not self._errors.has_key('bark_volume'):
                from django.forms.util import ErrorList
                self._errors['bark_volume'] = ErrorList()
            self._errors['bark_volume'].append('must be louder!')

That works on forms, at least. Never tried it on the model itself, but the methodology should be the same. However, from the Django docs:

When you use a ModelForm, the call to is_valid() will perform these validation steps for all the fields that are included on the form. (See the ModelForm documentation for more information.) You should only need to call a model’s full_clean() method if you plan to handle validation errors yourself, or if you have excluded fields from the ModelForm that require validation.

And...

Note that full_clean() will not be called automatically when you call your model’s save() method, nor as a result of ModelForm validation. You’ll need to call it manually when you want to run model validation outside of a ModelForm.

So, basically, unless you have a really good reason to do field cleaning on the model, you should do it on the form instead. The code for that would look like:

class DogForm(forms.ModelForm):

    def clean(self):
        bark_volume = self.cleaned_data.get('bark_volume')
        if bark_volume < 5:
            if not self._errors.has_key('bark_volume'):
                from django.forms.util import ErrorList
                self._errors['bark_volume'] = ErrorList()
            self._errors['bark_volume'].append('must be louder!')

        return self.cleaned_data

And that will work, for sure.