Django ModelForm make field from other fields

Question

I have these models

class Color(models.Model):
    code = models.CharField(max_length=7, unique=True)
    name = models.CharField(max_length=100)
class Tshirt(models.Model):
    name = models.CharField(max_length=100)
    color = models.ForeignKey(Color)

And I have this form

class TshirtForm(forms.ModelForm):
    color_code = forms.CharField(min_length=7, max_length=7)
    class Meta:
        model = Tshirt
        fields = ('name',)

How can I get the Color object from the color_code field and save that as the color of the new tshirt when the modelform is saved?

Answer 1

If you want your users to choose a color just extend the fields

class TshirtForm(forms.ModelForm):
    class Meta:
        model = Tshirt
        fields = ('name', 'color')

This will give you a select field in your form. Just make sure you add some colors for your users to choose from.

But if you want your users to "create" new colors, you should use two forms, one for color and the other one for the Tshirt. It's way simpler, than trying to do all in one form.

UPDATE:

Ok, update your form like this:

class TshirtForm(forms.ModelForm):
    color_code = forms.CharInput()

    class Meta:
        model = Tshirt
        fields = ('name', 'color')
        widget = {'color': forms.HiddenInput(required=False)}

    def clean(self, *args, **kwargs):
        # If users are typing the code, better do some validation
        try:
            color = Color.objects.get(
                code=self.cleaned_data.get('color_code')
            )
        except (ObjectDoesNotExist, MultipleObjectsReturned):
            raise forms.ValidationError('Something went wrong with your code!')
        else:
            # Update the actual field
            self.cleaned_data['color'] = color.id