I'm going to let the Django docs do a lot of the heavy lifting in this TIL and quote them liberally:
Assume these models:
from django.db import models
class Author(models.Model):
name = models.CharField(max_length=100)
class Book(models.Model):
author = models.ForeignKey(Author, on_delete=models.CASCADE)
title = models.CharField(max_length=100)
If you want to create a formset that allows you to edit books belonging to a particular author, you could do this:
>>> from django.forms import inlineformset_factory
>>> BookFormSet = inlineformset_factory(Author, Book, fields=["title"])
>>> author = Author.objects.get(name="Mike Royko")
>>> formset = BookFormSet(instance=author)
Subclass BaseInlineFormSet
and override the method:
from django.forms import BaseInlineFormSet
class CustomInlineFormSet(BaseInlineFormSet):
def clean(self):
super().clean()
# example custom validation across forms in the formset
for form in self.forms:
# your custom formset validation
...
Then, when creating the formset, pass your custom formset as an argument to inlineformset_factory
:
>>> from django.forms import inlineformset_factory
>>> BookFormSet = inlineformset_factory(
... Author, Book, fields=["title"], formset=CustomInlineFormSet
... )
>>> author = Author.objects.get(name="Mike Royko")
>>> formset = BookFormSet(instance=author)
Example: a Friendship
model:
class Friendship(models.Model):
from_friend = models.ForeignKey(
Friend,
on_delete=models.CASCADE,
related_name="from_friends",
)
to_friend = models.ForeignKey(
Friend,
on_delete=models.CASCADE,
related_name="friends",
)
length_in_months = models.IntegerField()
To solve, pass the fk_name
argument to inlineformset_factory
:
>>> FriendshipFormSet = inlineformset_factory(
... Friend, Friendship, fk_name="from_friend", fields=["to_friend", "length_in_months"]
... )
def manage_books(request, author_id):
author = Author.objects.get(pk=author_id)
BookInlineFormSet = inlineformset_factory(Author, Book, fields=["title"])
if request.method == "POST":
formset = BookInlineFormSet(request.POST, request.FILES, instance=author)
if formset.is_valid():
formset.save()
# Do something. Should generally end with a redirect. For example:
return HttpResponseRedirect(author.get_absolute_url())
else:
formset = BookInlineFormSet(instance=author)
return render(request, "manage_books.html", {"formset": formset})