I found an example of how to do this in this blog post. Below I've rewritten the example using my Publisher/Book/BookImage models, and generic class-based views, for future reference.
The form also allows the user to edit the titles of the Books, which wasn't what I originally wanted, but this seems easier than not doing it; the inline Book forms require at least one field each, so we may as well include the Book's title.
Also, to see how this worked, I've put together a small Django project using this code, and a little more detail, available on GitHub.
models.py:
from django.db import models
class Publisher(models.Model):
name = models.CharField(max_length=255)
class Book(models.Model):
title = models.CharField(max_length=255)
publisher = models.ForeignKey('Publisher', on_delete=models.CASCADE)
class BookImage(models.Model):
book = models.ForeignKey('Book', on_delete=models.CASCADE)
image = models.ImageField(max_length=255)
alt_text = models.CharField(max_length=255)
forms.py:
from django.forms.models import BaseInlineFormSet, inlineformset_factory
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 a custom `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 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
# This is the formset for the Books belonging to a Publisher and the
# BookImages belonging to those Books.
PublisherBooksWithImagesFormset = inlineformset_factory(
Publisher,
Book,
formset=BaseBooksWithImagesFormset,
fields=('title',),
extra=1)
views.py:
from django.http import HttpResponseRedirect
from django.views.generic import FormView
from django.views.generic.detail import SingleObjectMixin
from .forms import PublisherBooksWithImagesFormset
from .models import Publisher, Book, BookImage
class PublisherUpdateView(SingleObjectMixin, FormView):
model = Publisher
success_url = 'publishers/updated/'
template_name = 'publisher_update.html'
def get(self, request, *args, **kwargs):
# The Publisher whose Books we're editing:
self.object = self.get_object(queryset=Publisher.objects.all())
return super().get(request, *args, **kwargs)
def post(self, request, *args, **kwargs):
# The Publisher whose Books we're editing:
self.object = self.get_object(queryset=Publisher.objects.all())
return super().post(request, *args, **kwargs)
def get_form(self, form_class=None):
"Use our formset of formsets, and pass in the Publisher object."
return PublisherBooksWithImagesFormset(
**self.get_form_kwargs(), instance=self.object)
def form_valid(self, form):
form.save()
return HttpResponseRedirect(self.get_success_url())
templates/publisher_update.html:
{% extends 'base.html' %}
{% block content %}
<form action="" method="post" enctype="multipart/form-data">
{% for hidden_field in form.hidden_fields %}
{{ hidden_field.errors }}
{{ hidden_field }}
{% endfor %}
{% csrf_token %}
{{ form.management_form }}
{{ form.non_form_errors }}
{% for book_form in form.forms %}
{# Output a Book form. #}
{% for hidden_field in book_form.hidden_fields %}
{{ hidden_field.errors }}
{% endfor %}
<table>
{{ book_form.as_table }}
</table>
{# Check if our `nested` property exists, with BookImage forms in it. #}
{% if book_form.nested %}
{{ book_form.nested.management_form }}
{{ book_form.nested.non_form_errors }}
{% for bookimage_form in book_form.nested.forms %}
{# Output the BookImage forms for this Book. #}
{% for hidden_field in bookimage_form.hidden_fields %}
{{ hidden_field.errors }}
{% endfor %}
<table>
{{ bookimage_form.as_table }}
</table>
{% endfor %}
{% endif %}
{% endfor %}
<input type="submit" value="Update books">
</form>
{% endblock content %}
