Django's formset to edit partly predefined data - django

Question

Here's my domain model:
class Seat(models.Model):
name = models.CharField(max_length=8)
class Event(models.Model):
...
class Occupation(models.Model):
event = models.ForeignKey(Event, related_name='occupations')
seat = models.ForeignKey(Seat)
number = models.CharField(max_length=20)
(Seat is a small table, like 5-10 records.)
We have an UI requirements for a event edit page to look like this:
[1-01] [enter number]
[1-02] [enter number]
[1-03] [enter number]
[2-01] [enter number]
[2-02] [enter number]
[2-03] [enter number]
User navigates to event's occupation page where they see a list of all seats from system and prompted to fill numbers from the external source into the system.
Since the seats table is pretty small and to prevent errors like choosing same seat twice, we're required to display all seats pre-fill into the form and locked, so the user can't change seat selection and only limited to enter corresponding numbers.
Also, seats can be added or removed, so we can't make a "static" form with 6 predefined rows.
I suppose it should be a Django's inline model formset with a form like
class OccupationForm(forms.ModelForm):
class Meta:
model = Occupation
fields = ('seat', 'number')
...
But I'm not sure how should I display a prefilled form, prevent an user from changing seats (and not just a client-side locking via disabled or javascript)

Answer 1

First set seat widget to HiddenInput and add the seat_name property to the form. This property will be used later in the HTML template:
class OccupationForm(forms.ModelForm):
class Meta:
model = Occupation
fields = ('seat', 'number')
widgets = {'seat': forms.HiddenInput}
def __init__(self, *args, **kwargs):
super(OccupationForm, self).__init__(*args, **kwargs)
self.fields['number'].required = False
self.seat_name = self.initial['seat'].name
Then populate initial data with the seats and numbers for the event. Pass this initial to the formset. Validate and save formset as usual:
from django.forms.formsets import formset_factory
def update_seats(request, event_id):
event = Event.objects.get(pk=event_id)
numbers = dict((o.seat, o.number) for o in event.occupations.all())
initial = [{'seat': seat, 'number': numbers.get(seat, '')}
for seat in Seat.objects.all()]
OccupationFormSet = formset_factory(OccupationForm,
min_num=len(initial), validate_min=True,
max_num=len(initial), validate_max=True,
extra=0)
if request.method == 'POST':
formset = OccupationFormSet(request.POST, initial=initial)
if formset.is_valid():
for form in formset:
seat = form.initial['seat']
number = form.cleaned_data.get('number', '').strip()
if number:
Occupation.objects.update_or_create(
event=event, seat=seat,
defaults={'number': number})
else:
Occupation.objects.filter(event=event, seat=seat).delete()
return redirect('.')
else:
formset = OccupationFormSet(initial=initial)
return render(request, 'update_seats.html', {'formset': formset})
And update_seats.html template in which we show seat name as {{ form.seat_name }}:
<form action="" method="post">
{% csrf_token %}
<table>
{{ formset.management_form }}
<tr>
<th>Seat</th>
<th>Number</th>
</tr>
{% for form in formset %}
<tr>
<td>[{{ form.seat_name }}]{{ form.seat }}</td>
<td>{{ form.number }}</td>
</tr>
{% endfor %}
</table>
<button>Update</button>
</form>