forms.py

from django.forms.models import BaseInlineFormSet, inlineformset_factory
from django.utils.translation import gettext_lazy as _

from publishing.utils.forms import is_empty_form, is_form_persisted
from .models import Publisher, Book, BookImage


# The formset for editing the BookImages that belong to a Book.
BookImageFormset = inlineformset_factory(
    Book, BookImage, fields=("image", "alt_text"), extra=1
)


class BaseBooksWithImagesFormset(BaseInlineFormSet):
    """
    The base formset for editing Books belonging to a Publisher, and the
    BookImages belonging to those Books.
    """

    def add_fields(self, form, index):
        super().add_fields(form, index)

        # Save the formset for a Book's Images in the nested property.
        form.nested = BookImageFormset(
            instance=form.instance,
            data=form.data if form.is_bound else None,
            files=form.files if form.is_bound else None,
            prefix="bookimage-%s-%s"
            % (form.prefix, BookImageFormset.get_default_prefix()),
        )

    def is_valid(self):
        """
        Also validate the nested formsets.
        """
        result = super().is_valid()

        if self.is_bound:
            for form in self.forms:
                if hasattr(form, "nested"):
                    result = result and form.nested.is_valid()

        return result

    def clean(self):
        """
        If a parent form has no data, but its nested forms do, we should
        return an error, because we can't save the parent.
        For example, if the Book form is empty, but there are Images.
        """
        super().clean()

        for form in self.forms:
            if not hasattr(form, "nested") or self._should_delete_form(form):
                continue

            if self._is_adding_nested_inlines_to_empty_form(form):
                form.add_error(
                    field=None,
                    error=_(
                        "You are trying to add image(s) to a book which "
                        "does not yet exist. Please add information "
                        "about the book and choose the image file(s) again."
                    ),
                )

    def save(self, commit=True):
        """
        Also save the nested formsets.
        """
        result = super().save(commit=commit)

        for form in self.forms:
            if hasattr(form, "nested"):
                if not self._should_delete_form(form):
                    form.nested.save(commit=commit)

        return result

    def _is_adding_nested_inlines_to_empty_form(self, form):
        """
        Are we trying to add data in nested inlines to a form that has no data?
        e.g. Adding Images to a new Book whose data we haven't entered?
        """
        if not hasattr(form, "nested"):
            # A basic form; it has no nested forms to check.
            return False

        if is_form_persisted(form):
            # We're editing (not adding) an existing model.
            return False

        if not is_empty_form(form):
            # The form has errors, or it contains valid data.
            return False

        # All the inline forms that aren't being deleted:
        non_deleted_forms = set(form.nested.forms).difference(
            set(form.nested.deleted_forms)
        )

        # At this point we know that the "form" is empty.
        # In all the inline forms that aren't being deleted, are there any that
        # contain data? Return True if so.
        return any(not is_empty_form(nested_form) for nested_form in non_deleted_forms)


# This is the formset for the Books belonging to a Publisher and the
# BookImages belonging to those Books.
#
# You'd use this by passing in a Publisher:
#     PublisherBooksWithImagesFormset(**form_kwargs, instance=self.object)
PublisherBooksWithImagesFormset = inlineformset_factory(
    Publisher,
    Book,
    formset=BaseBooksWithImagesFormset,
    # We need to specify at least one Book field:
    fields=("title",),
    extra=1,
    # If you don't want to be able to delete Publishers:
    # can_delete=False
)