Good ways to sort a queryset? - Django

Question

what I\'m trying to do is this:

• get the 30 Authors with highest score ( Author.objects.order_by(\'-score\')[:30] )

• order the au

Answer 1

I just wanted to illustrate that the built-in solutions (SQL-only) are not always the best ones. At first I thought that because Django's QuerySet.objects.order_by method accepts multiple arguments, you could easily chain them:

ordered_authors = Author.objects.order_by('-score', 'last_name')[:30]

But, it does not work as you would expect. Case in point, first is a list of presidents sorted by score (selecting top 5 for easier reading):

>>> auths = Author.objects.order_by('-score')[:5]
>>> for x in auths: print x
... 
James Monroe (487)
Ulysses Simpson (474)
Harry Truman (471)
Benjamin Harrison (467)
Gerald Rudolph (464)

Using Alex Martelli's solution which accurately provides the top 5 people sorted by last_name:

>>> for x in sorted(auths, key=operator.attrgetter('last_name')): print x
... 
Benjamin Harrison (467)
James Monroe (487)
Gerald Rudolph (464)
Ulysses Simpson (474)
Harry Truman (471)

And now the combined order_by call:

>>> myauths = Author.objects.order_by('-score', 'last_name')[:5]
>>> for x in myauths: print x
... 
James Monroe (487)
Ulysses Simpson (474)
Harry Truman (471)
Benjamin Harrison (467)
Gerald Rudolph (464)

As you can see it is the same result as the first one, meaning it doesn't work as you would expect.