Django forms class that does not refresh - django

Question

I have noticed a weird behavior in one of my Django applications, running with apache/mod_wsgi. There is a screen that displays a form, basically a dropown list with a list of availability to schedule a given site, computed from the difference between a given weekly capacity (3 sites/wk) and the total number of sites already scheduled at a given week.
This form (ScheduleForm) is rendered from following view (followup/views.py):
def schedule(request, site_id):
site = Site.objects.get(pk=site_id)
if request.method == 'POST':
form = ScheduleForm(request.POST)
if form.is_valid():
(year, week) = request.POST['available_slots'].split('/')
site.scheduled = week2date(int(year), int(week[1:]))
site.save()
return HttpResponseRedirect('/stats/')
else:
form = ScheduleForm()
return render_to_response('followup/schedule_form.html',{
'form': form,
'site': site
}, context_instance=RequestContext(request))
Here is the form class (followup/forms.py):
class ScheduleForm(forms.Form):
"""
Temporary lists
"""
schedules = Site.objects.filter(
scheduled__isnull=False
).values('scheduled').annotate(Count('id')).order_by('scheduled')
integration = {}
available_integration = []
# This aggregates all schedules by distinct weeks
for schedule in schedules:
if schedule['scheduled'].strftime('%Y/W%W') in integration.keys():
integration[schedule['scheduled'].strftime('%Y/W%W')] += schedule['id__count']
else:
integration[schedule['scheduled'].strftime('%Y/W%W')] = schedule['id__count']
for w in range(12): # Calculates availability for the next 3 months (3months*4 weeks)
dt = (date.today() + timedelta(weeks=w)).strftime('%Y/W%W')
if dt in integration.keys():
capacity = 3-integration[dt]
else:
capacity = 3
if capacity>0:
available_integration.append([dt, capacity])
"""
Form
"""
available_slots = forms.ChoiceField(
[[slot[0], '%s (%s slots available)' % (slot[0], slot[1])] for slot in available_integration]
)
class IntegrateForm(forms.Form):
integrated_on = forms.DateField(widget=AdminDateWidget())
This actually works fine but the only problem is that the list of availability is not refreshed when a site is scheduled, unless I restart the apache process each time I schedule a site.
It's like if the availability list would be cached by the form class...
Any idea would be warmly welcomed. Thank you in advance for any kind of help.

Answer 1

This has to do with how python works and not django.
This code below
class ScheduleForm(forms.Form):
"""
Temporary lists
"""
schedules = Site.objects.filter(
scheduled__isnull=False
).values('scheduled').annotate(Count('id')).order_by('scheduled')
integration = {}
available_integration = []
will be evalutated only once - when the server starts.
You shouldn't do these things on the class level, but on the instance level.
Most likely inside the __init__ method of your form.
See the examples below:
Django - change min_length in form __init__?
django model form, restrict choices based on value in ForeignKey model
Django "dynamic" verification form (updated)

Answer 2

I have modified my code as follows and it's now working like a charm :) I provide it here in case it helps anyone with a similar problem.
class ScheduleForm(forms.Form):
available_slots = forms.ChoiceField()
def __init__(self, *args, **kwargs):
super(ScheduleForm, self).__init__(*args, **kwargs)
schedules = Site.objects.filter(
scheduled__isnull=False
).values('scheduled').annotate(Count('id')).order_by('scheduled')
integration = {}
available_integration = []
# This aggregates all schedules by distinct weeks
for schedule in schedules:
if schedule['scheduled'].strftime('%Y/W%W') in integration.keys():
integration[schedule['scheduled'].strftime('%Y/W%W')] += schedule['id__count']
else:
integration[schedule['scheduled'].strftime('%Y/W%W')] = schedule['id__count']
for w in range(12): # Calculates availability for the next 3 months (3months*4 weeks)
dt = (date.today() + timedelta(weeks=w)).strftime('%Y/W%W')
if dt in integration.keys():
capacity = 3-integration[dt]
else:
capacity = 3
if capacity>0:
available_integration.append([dt, capacity])
self.fields['available_slots'].choices = [[slot[0], '%s (%s slots available)' % (slot[0], slot[1])] for slot in available_integration]