My goal was to apply a custom queryset to a foreign key field. When the field is in a single model form, it was pretty clear to me how to proceed. However, when the field in question is part of a ModelFormset, I wasn’t seeing the way. Oddly enough, it came to me right before bed one night – iterate through the forms in the formset to apply the queryset to each one. Here’s how I handled each case.<\/p>\n
In this application, there is a one-to-many relationship between Event and Rsvp, and a one-to-many between Rsvp and Seat<\/p>\n
(snippet from views.py)<\/p>\n
## build the querysets\r\n event_queryset = Event.futures.filter(institution=inst_id)\r\n person_queryset = Person.objects.filter(institution=inst_id) \r\n\r\n ## create the formset\r\n SeatFormSet = inlineformset_factory(Rsvp, Seat, form=SeatForm, can_delete=True, extra=3)\r\n\r\n ...\r\n \r\n ## instantiate the form and formset\r\n rsvpform = RsvpForm(instance=rsvp)\r\n seatformset = SeatFormSet(instance=rsvp)\r\n\r\n ## Apply the queryset to the master form\r\n rsvpform.fields['event'].queryset = event_queryset\r\n\r\n ## Apply the queryset to each form in the formset\r\n for form in seatformset.forms:\r\n form.fields['person'].queryset = person_queryset<\/pre>\nIt’s important to note that the querysets must be applied each time the form and formset are instantiated in your view code in order for the validation to work correctly.<\/p>\n
In the for statement, I first tried iterating on the formset itself, but I was told that it was not iterable. A little perusal of the Django code for formsets showed me that the forms variable in the model was the object to use instead.<\/p>\n
I’d love to hear your comments on this technique.<\/p>\n","protected":false},"excerpt":{"rendered":"
My goal was to apply a custom queryset to a foreign key field. When the field is in a single model form, it was pretty clear to me how to proceed. However, when the field in question is part of a ModelFormset, I wasn’t seeing the way. Oddly enough, it came to me right before … <\/p>\n