Question

I have a formset in django that uses a model with a one to many relationship. Many attendees can attend a single event.

I am sending the ‘many’ part of the model in a formset. The problem is that the data is returned with no primary key set. I am getting a validation error because the formset primary key data is not set.

Back in my view, I know what the primary key is supposed to be. And i want to set it before validation. Either that or set the value before I send out the form for display. But I don’t know how to set it in the formset data.

In the code below, foreign key is event.

Option 1: Set the foreign key before showing the form:

#models.py  - note 2 foreign keys
class Attendee(models.Model):
    event = models.ForeignKey(Event)
    sponsor = models.ForeignKey(Customer)
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30) 

# forms.py
class AttendeeForm(forms.ModelForm): 
  event = forms.IntegerField(required=True, widget=forms.HiddenInput()) 

  class Meta: 
    model = Attendee 
    fields = ( 'last_name', 'first_name', ) 
    exclude = ('event', )  # excluded so user can't set foreign key

# views.py
event = get_object_or_404(Event, id=event_id)
AttendeeFormSet = inlineformset_factory(Event, Attendee, form=AttendeeForm, extra=1)
formset = AttendeeFormSet(instance=event, prefix='attendees')
# Error on form submit:  
#  Returns and redisplays the form along with message.
#  (Hidden field event) The inline foreign key did not match the parent instance primary key.


#  I also tried:  
#AttendeeFormSet = inlineformset_factory(Event, Customer, Attendee, form=AttendeeForm, extra=1)
# which gave error: 
# inlineformset_factory() got multiple values for keyword argument 'form'

Option 2: Set the foreign key on the return POST. Note even though data is present, the form is not valid because foreign key is not set.

formset = AttendeeFormSet(request.POST, request.FILES, prefix='attendees')
i=0
for form in formset.forms:
   # How can I set the foreign key (event) field here?
   pdb.set_trace()

if formset.is_valid():
   attendees = formset.save_all()


(Pdb) p form.fields
{'last_name': <django.forms.fields.CharField object at 0xaa44a2c>, 
'first_name':    <django.forms.fields.CharField object at 0xaa449ec>,  
'event': <django.forms.fields.IntegerField object at 0xaa44fec>}
(Pdb) 

What is the best way to fix my foreign key problem in my formset? If Option 2 How do I set this field before I test is_valid?

Answer 1

Since this is a formset representing a foreign key relationship, you should use inlineformset_factory to construct the class. That will take care of setting the FKs for you:

AttendeeFormSet = formset_factory(Event, Attendee, form=AttendeeForm)
...
formset = AttendeeFormSet(instance=my_event)