Make inlineformset in django required

Question

Hi,

I am new to django (until now, I used the symfony PHP Framework). My problem is this: I have a model Event and model Date. The Date has a foreign key to Event, so that an Event may (or should) have one or more Dates.

Now I want to have a form to create Events and this form should include a subform for adding one corresponding Date (more dates should be added later, if the Event has more than one date).

I used the inlineformset to realize the Date subform, but if no Date is being entered, no error occurs and the Event is being saved without a Date. All I want is to make this inlineformset required or to say, that there has to be at lease (and only) one inlineformset.

I found these questions, but none of the answers helped me:

• http://stackoverflow.com/questions/877723/inline-form-validation-in-django
• http://stackoverflow.com/questions/2406537/django-formsets-make-first-required

Any hints for me?

EDIT: I need this for the frontend, not for the backend. The first link covers it for the admin backend.

EDIT2: Some sourcecode added

MandatoryInlineFormSet.py:

from django.forms.models import BaseInlineFormSet
from django import forms

class MandatoryInlineFormSet(BaseInlineFormSet):
    def clean(self):
        # get forms that actually have valid data
        count = 0
        for form in self.forms:
            try:
                if form.cleaned_data:
                    count += 1
            except AttributeError:
                # annoyingly, if a subform is invalid Django explicity raises
                # an AttributeError for cleaned_data
                pass
        if count < 1:
            raise forms.ValidationError('You must have at least one order')

event.py:

from [...]
def new(request):
    DateFormset = inlineformset_factory(
            Event,
            Date,
            can_delete=False,
            extra=1,
            max_num=1,
            formset=MandatoryInlineFormSet,
            )

    if request.POST:
        form = EventForm(request.POST)
        date_formset = DateFormset(request.POST)
        if form.is_valid():
            event = form.save(commit=False)
            date_formset = DateFormset(request.POST, instance=event)
            if date_formset.is_valid():
                event.save()
                date_formset.save()
                return HttpResponseRedirect(reverse('frontpage'))
    else:
        form = EventForm()
        date_formset = DateFormset()
    return render_to_response('event/new.html', {
        'form': form,
        'date_formset': date_formset,
        }, context_instance=RequestContext(request))

event/new.html:

[...]
<form action="{% url new-event %}" method="post">
    {% csrf_token %}
    {{ form.as_p }}

    {{ date_formset.management_form }}
    {% for date_form in date_formset.forms %}
        {{ date_form.as_p }}
    {% endfor %}


    <input type="submit" value="{% trans "Create event" %}"/>
</form>
[...]

Best regards, sewid