Question bank

Pick an answer to see if you're right — with an explanation.

DjangoMedium

Why should `success_url` on a class-based view use `reverse_lazy`?

areverse() is deprecated

bIt caches the URL for faster redirects

cIt works with POST only

dThe URLconf isn't loaded when the class attribute is evaluated at import time

DjangoHard

How many database queries does this run?

qs = Post.objects.filter(published=True)
qs = qs.order_by('-created')
for p in qs[:5]:
    print(p.title)

aOne, when the loop starts iterating

bTwo, one per queryset line

cThree

dSix, one per post plus one

DjangoHard

How many queries does this loop run for 50 orders (no other optimisation)?

for o in Order.objects.all():
    print(len(o.items.all()))

c51

d100

DjangoHard

When should a project switch to a custom user model?

aOnly after real users exist in the database

bAt the start, before the first migration, by setting AUTH_USER_MODEL

cNever; Django forbids it

dAny time, it is a one-line change with no data impact

DjangoHard

Which statement decrements stock safely even if two requests run at the same moment?

ap.stock = p.stock - 1; p.save()

bProduct.objects.filter(pk=p.pk).update(stock=F('stock') - 1)

cp.refresh_from_db(); p.stock -= 1; p.save()

dProduct.objects.get(pk=p.pk).stock -= 1