Passing initial into Django's ModelFormSet

Question

I have a model formset that I need to pass the keyword initial in to (to have some initial values in the formset, such as date set to today).

As far as I can tell, the queryset argument (which defaults to YourModel.objects.all()) overrides this ability for initial empty forms to be created.

I specified the queryset as: YourModel.objects.none(), which prevents it from filling in the formset with entries from the database, but I still can't figure out how to pass initial in effectively.

Do I need to subclass a method from ModelForm?

Answer 1

You are passing an empty queryset to ModelFormset.

ExampleModelFormSet = modelformset_factory(ExampleModel, extra=2)
formset = ExampleModelFormSet(queryset=ExampleModel.objects.none(),
                          initial=[{'name': 'Some Name'},
                                   {'name': 'Another Name'}])

which is indeed the way to achieve what you want. It makes sense to pass an empty queryset, else initial values will override the model's database value.

And if I suppose, you are passing a non-empty queryset, and yet want your extra forms to be filled will initial values, you can override the Formset.

from django.forms.models import modelformset_factory  
ExampleFormset = modelformset_factory(OpenIDProfile, extra=3)

class myFormset(ExampleFormset):

    def _construct_form(self, i, **kwargs):
        """
        Instantiates and returns the i-th form instance in a formset.
        """
        if self.is_bound and i < self.initial_form_count():
            pk_key = "%s-%s" % (self.add_prefix(i), self.model._meta.pk.name)
            pk = self.data[pk_key]
            pk_field = self.model._meta.pk
            pk = pk_field.get_db_prep_lookup('exact', pk)
            if isinstance(pk, list):
                pk = pk[0]
            kwargs['instance'] = self._existing_object(pk)
        if i < self.initial_form_count() and not kwargs.get('instance'):
            kwargs['instance'] = self.get_queryset()[i]

        defaults = {'auto_id': self.auto_id, 'prefix': self.add_prefix(i)}
        if self.data or self.files:
            defaults['data'] = self.data
            defaults['files'] = self.files
        # Check to confirm we are not overwriting the database value.
        if not i in range(self.initial_form_count()) and self.initial:
            try:
                defaults['initial'] = self.initial[i - self.initial_form_count()]
            except IndexError:
                pass
        # Allow extra forms to be empty.
        if i >= self.initial_form_count():
            defaults['empty_permitted'] = True
        defaults.update(kwargs)
        form = self.form(**defaults)
        self.add_fields(form, i)        
        return form

Note: initial is list of dicts. Its desirable to have items in list exactly equal to the number of extra.

Answer 2

New in Django 1.4 ...if you set initial on a modelformset it now only applies to the 'extra' forms, not those bound to instances from the queryset:

https://docs.djangoproject.com/en/dev/topics/forms/modelforms/#providing-initial-values

So the various hacks above are no longer necessary and using initial is the answer.

Answer 3

The best way I've found to do this is to just manually adjust the formset object's "extra" attribute after initialization. This has been tested and works in Django 1.9.

ExampleModelFormSet = modelformset_factory(ExampleModel, extra=1)
formset = ExampleModelFormSet(initial=[{'name': 'Some Name'},
                                       {'name': 'Another Name'}])
formset.extra = 3

This will spit out 3 forms (2 prepopulated and 1 blank).

If you want something more dynamic (e.g. initial is a var calculated somewhere else), you can do something like this:

ExampleModelFormSet = modelformset_factory(ExampleModel, extra=1)
formset = ExampleModelFormSet(initial=initial)
formset.extra += len(initial)

Hope that helps.