(All tags.)
QuerySetsSometimes code depends on the order of a QuerySet whilst not specifying an order. This can lead to random, flaky test failures because databases can return rows in any order when none is specified. The problem is made worse by some databases, notably PostgreSQL, which nearly always return rows in insert order, but occasionally use a different order when a table has had recent deletions.
json_script for pre-serialized JSON stringsDjango’s json_script template filter is a convenient and safe way to pass a larger amount of data to JavaScript. I covered it in my post last year How to Safely Pass Data to JavaScript in a Django Template.
format_html()Can you spot the problem with this Django snippet?
Django’s template engine allows you to augment template contexts with context processors. These are functions that take the current request and return a dictionary to be merged into the context:
Here’s an application of “test smarter, not harder”, as per Luke Plant’s post. I came up with this recently whilst working on my client Silvr’s project, and I’m pretty proud of it. It should apply to any project using Django’s admin.
Your Django project’s startup time impacts how smooth it is to work with. Django has to restart your project every time you run a management command and when runserver reloads. This involves importing all your apps, and thus all the modules that they import.
If you upgrade to Django 4.2, you may see system check warnings like:
I just released django-upgrade 1.13.0. The headline features are some new fixers targeting Django 4.2, which is currently in alpha.
Here are some potential mistakes made with Django settings that you can avoid.
Here are some Django-related deals for this year’s Black Friday (25th Nov) and Cyber Monday (28th Nov), including my own. For more deals on general Python-related products, see Trey Hunner’s post.
Python 3.11 only made one change to unittest, but it’s a good one: context manager methods. These methods can simplify setup and teardown logic in many cases, such as dynamic use of unittest.mock.
I just released version 1.11.0 of django-upgrade, a tool for automatically upgrading your Django project code. This release contains a lot of new features and fixes, thanks to new contributors including those at the Djangocon Europe sprints. Let’s look at the top changes.
The Django 4.1 release notes feature this short, innocent-looking note:
In data import processes it’s often useful to have a “dry run” mode, that runs through the process but doesn’t actually save the data. This can allow you to check for validity and gather statistics, such as how many records already exist in the database. In this post, we’ll look at how to implement a dry run mode in Django by using a database transaction and rolling it back.
You want to pass your data from your Django view to JavaScript, in your template. And, you want to do it securely, with no risk of accidentally allowing malicious code injection. Great, this is the post for you!
partial() with transaction.on_commit() to avoid late-binding bugsDjango’s transaction.on_commit() allows you to run a function after the current database transaction is committed. This is useful to ensure that actions with external services, like sending emails, don’t run until the relevant data is definitely saved.
Normally your Django project’s deploy process runs the migrate command, and that takes care of updating your database as necessary. Especially on smaller databases, Django’s migration system can “just do it” for you.
Python’s requests package is very popular. Even if you don’t use it directly, it’s highly likely one of your dependencies does.
Slow queries happen, and when they do, it can be tough to dissect why they’re slow. This difficulty is compounded by using Django’s ORM, since it generates the SQL for you, so you may have little idea of the actual queries “under the hood”.
HTCPCP, or Hyper Text Coffee Pot Control Protocol, was published as an April Fool’s joke 24 years ago today. It’s an HTTP extension for controlling coffee pots, and whilst it is a joke, it appears in various places around the web.
It’s all too easy to forget to pass a variable to your template or make a typo in a variable name. Unfortunately, it can be quite hard to debug such mistakes, since Django’s default behaviour is to ignore the problem and render an empty string.
get_user_model()Django’s authentication system, django.contrib.auth, provides a built-in User model class. You can swap this to a different class with the AUTH_USER_MODEL setting, most easily at the start of the project.
I’ve just released django-htmx 1.9.0. As part of this release, it now has a documentation site built with Sphinx, hosted on Read the Docs at django-htmx.readthedocs.io.
WhiteNoise is a simple solution to serving static assets. It lets you skip configuring a separate web server for your static assets, and serve them straight from Django. It’s a brilliant tool. I’ve used it for years on various projects, and I’ve recommended it many times, and mentioned it in several blog posts.
contrib.staticfilesSource maps are files that map your minified CSS or JavaScript back to the original code. They allow you to use your browser’s development tools to debug minified code as if it were the original. Also some error capture tools, such as Sentry, can use source maps to report errors for the original code.