Django order_by query set, ascending and descending

python

django

queryset

ordering

byAnton Shumikhin·Oct 26, 2024

Sort a Django QuerySet with .order_by(): 'field' for ascending, '-field' for descending.

Example:

# Once upon a time, we ordered in ascending road
ascending_qs = MyModel.objects.order_by('field')

# Then decided to walk down the descending Road
descending_qs = MyModel.objects.order_by('-field')

Logical primer to ordering

Understanding the guts of Django order_by makes using it a breeze.

Looking to order by a related model field? Here's how:

# Sorting party by related friends' age
queryset = MyModel.objects.order_by('relatedmodel__field')

Smushing multiple fields in order_by

Want to sort on several things? Chain them:

# Sorting concert by date (rock before pop), then by band name. Party on!
queryset = MyModel.objects.order_by('-date', 'name')

Setting a default ordering

Picky about your default list order? Set it up in the Meta class:

class MyModel(models.Model):
    # ... fields here ...

    class Meta:
        # It's like mama always said, 'Name first, age second.'
        ordering = ('name', '-age')

Dynamic ordering

Life changes and so can your order_by:

# Life's pretty vanilla...
order_field = 'field' # or '-field' for descending

# ...until it's not
queryset = MyModel.objects.order_by(order_field)

Digging deeper into `order_by`

Play with order_by. Understand it, bend it to your will. Here's how:

How ordering treats null values

Deal with those pesky null pointers:

# When life gives you nulls, sort them to the last
queryset = MyModel.objects.order_by('field', 'other_field')

# Unless you want 'em first. We don't judge.
queryset = MyModel.objects.order_by(F('field').asc(nulls_first=True))

Mind your performance

Remember, order_by can also mean wait_for_it on large datasets:

# Ordering for ants? Fast.
# Ordering for elephants? Umm...
large_query_set = LargeModel.objects.order_by('-date', 'category', 'name')

It's your order, flip it!

Don't let order_by control you. Exercise your right to reverse:

# Ordered pizza but felt like sushi? Just reverse!
queryset = MyModel.objects.order_by('field').reverse()

Advanced ordering methods

Master order_by, use it like you invented it. Here are cool tricks:

Null-safe fields with SQL expressions

Turn null feel-sorry-for-me into null look-at-me-nailing-it:

# When life gives you nulls, make zero lemonades!
queryset = MyModel.objects.annotate(null_safe_field=Coalesce('field_with_nulls', 0)).order_by('null_safe_field')

Optimising JOINs in ordering

Too many JOIN operations? Don't get stuck, get optimizing:

# Optimise queryset ordering with foreign key fields.
MyModel.objects.select_related('foreign_key_field').order_by('foreign_key_field__related_field')

Custom ordering functions

Conquer world, or just simply custom sort it:

# Be that nerdy party-goer who orders people by name length.
from django.db.models import Func
class Length(Func):
    function = 'LENGTH'

queryset = MyModel.objects.annotate(field_length=Length('name')).order_by('field_length')

Error-proofing

Remember, the only certainties in life are death and AttributeError:

# Well, we tried, and we caught. Life moves on.
try:
    queryset = MyModel.objects.order_by('nonexistent_field')
except FieldError:
    queryset = MyModel.objects.order_by('default_field')