Limit Django's inlineformset_factory to only create new objects

Question

I am using django's inline formset factory. To use the example in the docs,

author = Author.objects.get(pk=1)
BookFormSet = inlineformset_factory(Author, Book)
formset = BookFormSet(request.POST, instance=author)

will create an inline formset to edit books by a particular author.

I want to create a formset that only allows users to add new books by that author, not edit existing books. Is there a simple way to use inlineformset_factory to do this?

Answer 1

inlineformset_factory takes a formset kwarg, which defaults to BaseInlineFormSet. BaseInlineFormSet subclasses BaseModelFormSet, which defines a get_queryset method. If you create a BaseInlineFormSet subclass and override get_queryset to return EmptyQuerySet(), you should get what you're after. In the above example then, it would look like this:

from django.db.models.query import EmptyQuerySet
from django.forms.models import BaseInlineFormSet

class BaseInlineAddOnlyFormSet(BaseInlineFormSet):
    def get_queryset(self):
        return EmptyQuerySet()

author = Author.objects.get(pk=1)
BookFormSet = inlineformset_factory(Author, Book, formset=BaseInlineAddOnlyFormSet)
formset = BookFormSet(request.POST, instance=author)

Answer 2

Based on Jeremy Lewis and if you don't want to subclass BaseInlineFormSet, you can just give an empty queryset parameter to your BookFormSet.

See pseudo (untested) Django 1.6 code sample:

BookFormSet = inlineformset_factory(parent=Author, model=Book)
if request.method == "POST":
    formset = BookFormSet(request.POST, request.FILES, instance=author)
    if formset.is_valid():
        formset.save()
else:
    queryset = Book.objects.none() # does not allow to edit books
    formset = BookFormSet(instance=project, initial=initial, queryset=queryset)
return render(request, "add_book.html", { "formset": formset, })