nested inline implementation in ModelForm

admin.py

class MyForm(StackedInline.form):

    def __init__(self, *args, **kwargs):
        super(MyForm, self).__init__(*args, **kwargs)
        self.instance.form = self

    def is_valid(self):
        return super().is_valid() and self.nested.formset.is_valid()

    @cached_property
    def nested(self):
        modeladmin = ProductModelAdmin(self._meta.model, self.modeladmin.admin_site)

        # get formsets and instances for change/add view depending on the request
        formsets, instances = modeladmin._create_formsets(self.modeladmin.request, self.instance, change=self.instance.pk)

        # gets the inline from inline_formsets
        inline = modeladmin.get_inline_formsets(self.modeladmin.request, formsets[:1], instances[:1], self.instance)[0]

        # handles prefix
        inline.formset.prefix = f'{self.prefix}_{formsets[0].prefix}'.replace('-', '_')
        return inline