How to add custom fields to InlineFormsets?

Question

I'm trying to add custom fields to an InlineFormset using the following code, but the fields won't show up in the Django Admin. Is the InlineFormset too locked down to allow this? My print "ding" test fires as expected, I can print out the form.fields and see them all there, but the actual fields are never rendered in the admin.

admin.py

from django.contrib import admin
import models
from django.forms.models import BaseInlineFormSet
from django import forms
from forms import ProgressForm
from django.template.defaultfilters import slugify

class ProgressInlineFormset(BaseInlineFormSet):
    def add_fields(self, form, index):
        print "ding"
        super(ProgressInlineFormset, self).add_fields(form, index)
        for criterion in models.Criterion.objects.all():
            form.fields[slugify(criterion.name)] = forms.IntegerField(label=criterion.name)

class ProgressInline(admin.TabularInline):
    model = models.Progress
    extra = 8
    formset = ProgressInlineFormset

class ReportAdmin(admin.ModelAdmin):
    list_display = ("name", "pdf_column",)
    search_fields = ["name",]
    inlines = (ProgressInline,)

admin.site.register(models.Report, ReportAdmin)

Answer 1

I did it another way:

forms.py:

from django import forms
class ItemAddForm(forms.ModelForm):
    my_new_field = forms.IntegerField(initial=1, label='quantity')
    class Meta:
        model = Item

admin.py:

from django.contrib import admin
from forms import *
class ItemAddInline(admin.TabularInline):
    form = ItemAddForm

This works so far, I only need to override somehow the save method to handle this new field. See this: http://docs.djangoproject.com/en/dev/ref/contrib/admin/#form . It says that by default Inlines use BaseModelForm, which is send to formset_factory. It doesn't work for me, tried to subclass BaseModelForm with errors (no attribute '_meta'). So I use ModelForm instead.

Answer 2

You can do it by another way (Dynamic forms):

admin.py

class ProgressInline(admin.TabularInline):
    model = models.Progress
    extra = 8

    def get_formset(self, request, obj=None, **kwargs):
        extra_fields = {'my_field': forms.CharField()}
        kwargs['form'] = type('ProgressForm', (forms.ModelForm,), extra_fields)
        return super(ProgressInline, self).get_formset(request, obj, **kwargs)