How to validate the sum of a field of many inlineformset in a CreateView?

Question

I have a CreateView of a model with an inlineformset_factory of another model (4 rows, one of each child model). One of the child's model is 'Percentage'. Right now it saves bot the parent and the child model, but I don't have any validation on the percentage field, so the User can easily type '11', '34', '02' and '0' and it will save it.

I want to validate that, before saving anything, the sum of the percentage fields are 100%. My forms.py look like this:

class ParentForm(ModelForm):
    class Meta:
        model = Parent
        fields = ['name', 'observations']


class ChildCreateForm(ModelForm):
    class Meta:
        model = Child
        fields = ['percentage', 'material']

    def clean(self):
        cleaned_data = super(ChildCreateForm, self).clean()
        print(cleaned_data['percentage'])


ChildCreateFormCreateFormSet = inlineformset_factory(Parent, Child, form=ChildCreateForm, extra=4)

So far so good, I can validate every percentage row individually, but I want to validate the total sum.

Should I validate the form with Javascript? There is a way with Django? Or it is best a third option?

Answer 1

You can subclass BaseInlineFormSet and override the clean method. instance with a clean method.

from django.forms import BaseInlineFormSet

class BaseChildFormSet(BaseInlineFormSet):
    def clean(self):
        super().clean()
        total_percentage = sum(f.cleaned_data['percentage'] for f in self.forms)
        if total_percentage != 100:
            raise forms.ValidationError("Total percentage must be 100")

Then use your class when you create the formset class.

ChildCreateFormCreateFormSet = inlineformset_factory(Parent, Child, form=ChildCreateForm, formset= BaseChildFormSet, extra=4)

See the docs for more info.