Django Models with Choices as Integer - django

Question

I am trying to make a feedback app in Django, but I can not make my evaluations.
In my models.py, I have 5 choices from very bad to excellent. But I want them to be usable as numbers so I can evaluate the overall value.
After reading Set Django IntegerField by choices=... name I changed my Ratings from VERYBAD = 'Very bad' to VERYBAD = 1 but no I can't even save my value/form.
Feedback(models.Model):
event = models.ForeignKey(Event)
# Choice
VERYBAD = 'Very bad' #old
BAD = 2 #new
OKAY = 3
GOOD = 4
EXCELLENT = 5
RATING = (
(VERYBAD, 'Very bad'),
(BAD, 'Bad'),
(OKAY, 'Okay'),
(GOOD, 'Good'),
(EXCELLENT, 'Excellent'),
)
# The ratings
organisation = models.CharField(
max_length=9,
choices=RATING,
default=OKAY,
)
....
So in my view, I thought I can do the math but I can not.
def rating(request, event_id):
myevent = Event.objects.get(id=event_id)
feedback_items = Feedback.objects.filter(event=myevent)
num_of_items = len(feedback_items)
def evaluate(feedback_items):
# The overall rating
organisation = 0
for item in feedback_items:
organisation += item.organisation
organisation /= num_of_items
context = {'feedback_items':feedback_items,
'num_of_items': num_of_items,
'myevent': myevent,}
return render(request, 'feedback/rating.html', context)
`

Answer 1

You have to make organisation an IntegerField, obviously - else you can't hope to do integer operations. If you already have this in production, use a set of migrations to add a new IntegerField, populate it from the existing CharField values (using a dict for mapping old string values to new int values), and finally getting rid of the original field.
Also, you may want to learn how to properly use Django's ORM features like getting related models instances and performing aggregations at the DB level, ie:
from django.db.models import Sum, Count, Avg
def rating(request, event_id):
myevent = Event.objects.get(id=event_id)
# this is how you get related models...
feedback_items = myevent.feedback_set.all()
# and this is how you use SQL aggregation functions:
values = feedback_items.aggregate(
sum=Sum('organisation'),
count=Count('pk'),
avg=Avg('organisation')
)
# Now 'values' should be a dict with 'sum', 'count' and 'avg'
# keys, and values['avg'] should be equal to
# float(values['sum']) / values['count']
# FWIW you probably don't need the 'sum' field at all
# I mentionned it so you can check whether 'avg' value
# is correct...
context = {
'feedback_items':feedback_items,
'num_of_items': values['count'],
'avg': values['avg'],
'myevent': myevent,
}
# etc