Set instance of each form in Django model formset

Question

When working with Django model forms, I often do something like this:

def my_view(request):
    new_entry = MyModel(name='a')
    form = MyModelForm(instance=new_entry)
    ...

I want to do something similar with a modelformset. Something like this would be ideal:

def my_view(request):
    MyFormSet = modelformset_factory(MyModel, form=MyModelForm)
    new_entries = [MyModel(name='a'), MyModel(name='b')]
    formset = MyFormSet(instances=new_entries) # off course this does not work
    ...

Since the items are not stored in the database yet, I can't set the instances using a queryset. If I want to use initial I have to declare the fields in the form, which is not ideal and seems a bit hacky.

Any suggestions how I can set the instances of each modelform in a modelformset?

Answer 1

Ok, I think I've found a solution.

class FormSetWithInstances(BaseFormSet):
    def __init__(self, *args, **kwargs):
        self.instances = kwargs.pop('instances')
        super(FormSetWithInstances, self).__init__(*args, **kwargs)

    def get_form_kwargs(self, index):
        form_kwargs = super(FormSetWithInstances, self).get_form_kwargs(index)
        if index < len(self.instances):
            form_kwargs['instance'] = self.instances[index]
        return form_kwargs

Be careful when using this modelformsets or inlinemodelformsets, as the queryset will override the instance you set.