Django ModelForm with extra fields that are not in the model

Question

I have done a ModelForm adding some extra fields that are not in the model. I use these fields for some calcualtions when saving the form.

The extra fie

Answer 1

Ok I have resolved it. It seems that accessing the extra fields with cleaned_data['field_name'] raises a KeyError but using cleaned_data.get('field_name') works. That's weird because normal fields for the model can be accessed via cleaned_data['field_name'].

Update: No, it doesn't work. With get() it doesn't raise a KeyError but it sets a value of None because the extra fields are not in the cleaned_data dictionary.

Here is the code. In the templates there is an autocomplete, so in the form there is an "artist" field rendered as a CharField and an hidden IntegerField that will be autopopulated with the given artist id. In the clean_artist method I want to select the artist object and store it in the artist field of the form.

models.py

class Music(models.Model):
    artist = models.ForeignKey(Artist, related_name='music', blank=True, null=True)
    # other fields...

forms.py

class MusicForm(forms.ModelForm):
    artist_id = forms.IntegerField(label="", widget=forms.HiddenInput(), required=False)
    artist = forms.CharField(required=False)
    # other fields ...

    class Meta:
        model = Music

    def clean_artist(self):
        if self.cleaned_data.get('artist') == '':
            artist = None
        else:
            artist_id = self.cleaned_data.get('artist_id') # this returns always None because artist_id is not in cleaned_fields (this seemed to work with previous django versions but not with current SVN version)
            if artist_id != None:
                artist = Artist.objects.get(id=artist_id)
            else:
                artist = None

    return artist