Django 4.0 Is Out — Here Is Everything About It

TL;DR: Major features in 4.0 are data bases related e.g. example functional unique constraints for database functions, native redis support

Django 4.0 was released on the Dec 7, 2021

So, the Django Team has finally released Django 4.0. Lets deep deeper into some of the features:

1. Functional unique constraints¶

The new *expressions positional argument of UniqueConstraint() allows to create functional unique constraints on expressions and database functions. For example:

from django.db import models
from django.db.models import UniqueConstraint
from django.db.models.functions import Lower

class MyModel(models.Model):
    first_name = models.CharField(max_length=255)
    last_name = models.CharField(max_length=255)
    class Meta:
        constraints = [
            UniqueConstraint(
                Lower('first_name'),
                Lower('last_name').desc(),
                name='first_last_name_unique',
            ),
        ]

Functional unique constraints are added to models using the Meta.constraints option.

2. Redis cache backend¶

The new django.core.cache.backends.redis.RedisCache also allows a built-in support for caching with Redis. redis-py 3.0.0 or higher is required. In the past I used https://github.com/jazzband/django-redis lib.

3. Random testing order

Now it is possible to execute tests in a random order. You can achieve that by

from django.test.runner import DiscoverRunner


class TestRunner(DiscoverRunner):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        if self.shuffle is False:
            self.shuffle = None  # will generate a radom seed

4. Scrypt password hasher

A scrypt password hasher is more secure and recommended over the PBKDF2 algorithm. But it is not the default, as it requires OpenSSL 1.1 and additional memory.

A list of all new features can be found under https://docs.djangoproject.com/en/4.0/releases/4.0/