validate delete inline formset django

1class RequiredImageInlineFormset(forms.models.BaseInlineFormSet):
2    """ Makes inline fields required """
3
4    def clean(self):
5        # get forms that actually have valid data
6        count = 0
7        delete_checked = 0
8        for form in self.forms:
9            try:
10                if form.cleaned_data:
11                    count += 1
12                    if form.cleaned_data['DELETE']:
13                        delete_checked += 1
14                    if not form.cleaned_data['DELETE']:
15                        delete_checked -= 1
16            except AttributeError:
17                # annoyingly, if a subform is invalid Django explicity raises
18                # an AttributeError for cleaned_data
19                pass
20
21        # Case no images uploaded
22        if count < 1:
23            raise forms.ValidationError(
24                'At least one image is required.')
25
26        # Case one image added and another deleted
27        if delete_checked > 0 and ProductImage.objects.filter(product=self.instance).count() == 1:
28            raise forms.ValidationError(
29                "At least one image is required.")
30