Tags - django

An alternative to Enum for Choices

Those who've been reading my older posts may remember I showed how you could use Enum and IntEnum as a cleaner way to declare const-type values for choices lists in Django fields.

That solution never felt comfortable to me, because Enum values aren't simple values.

So after some playing around, and a brief look over the enum.py in python 3.5, I've come up with the following:

Django and Model Inheritance

I was recently helping someone with the seemingly easy task of getting a list of related sub-models. This was working with a "tree" structure, where the base model had a ForeignKey to itself.

Whilst django-model-utils and django-polymorphic provide solid implementations for this, I have derived my own solution and tuned it up.

This solution only works properly if there is only ever one sub-class for a given base class instance. Otherwise, it may behave contrary to expectations.

Django file name conventions

Conventions, not Rules

As many newcomers to Python discover, a lot of things they've lived with as rules in other languages [such as public/private members] ... and, conversely, some things they're accustomed to as conventions are now rules [like indenting].

Now, Django continues its history of embracing Pythonic ideals when it comes to filenames. Many frameworks are very strict about what goes where ... in almost all cases, Django couldn't care less.

Dynamic formsets with Django

Note: This post is still a Work In Progress. I am posting it now to help people with what I have, and seek feedback and furter input.

Recently a few people have been asking about managing dymanic numbers of FormSets in Django.

When we look at how Admin handles inlines we seee Django can handle this already.

Django Registration redux

So, 4 years ago [already??] I wrote a post about a shortcut to getting "User registration with verification email", using very little code by leveraging the password reset machinery built into Django.

Since then, of course, Django has moved on... and recently, the auth views were rewritten as class-based views, which changes the game entirely.

As a result, I've committed to providing here an updated version of the previous post.

Django semi-DRY Fields

DRY fields

So, your app is growing nicely, but you find yourself repeating the same field definition in a bunch of models. The models themselves have nothing to do with each other, so an abstract base class isn't a fit, but at various points you want, say, prices to always be the same configuration of DecimalField, or titles to always allow the same size.

So, you could sub-class the fields to produce your own pre-configured fields, but sometimes you want to vary them a little... this price is nullable, that title has help_text, and so on.

Environment driven config

Some years ago, I adapted the work of a coworker and released it as django-classy-settings, a way to define Django settings using a class, allowing a clean and easy way to derive local / production settings from a common base, and opening the way to allowing composition, too.

Recently I was faced with a similar problem at my current job, though not using Django this time.

Another big difference is my current job is using Python3.6 (and eager to move to 3.7 ASAP), opening other opportunities.

IntEnum for Choices in Django

So, we've all needed a choices list in Django at one time or another, right?

And from the docs we see the example code:

YEAR_IN_SCHOOL_CHOICES = (
    ('FR', 'Freshman'),
    ('SO', 'Sophomore'),
    ('JR', 'Junior'),
    ('SR', 'Senior'),
)

Dispelling Token Auth myths

Recently a friend commented on how Django might do more to support SPA applications, notably by having built-in support for authentication using JWTs.

This is not a new question, and recently I've been discussing with someone on IRC about JWT support in Django that was not tied to Django REST Framework.

I have frequently helped people on IRC having issues supporting token based auth in their APIs. But all too often they can't explain why they're using token auth or what problems it solve for them, just that they read somewhere it was needed. (Or worse, their Manager demanded it without justification.)

Modern Vanilla JS for cookie parsing

In a previous post I wrote a Vanilla JS function for parsing all the current cookies. Since then a couple of things have happened:

  1. I realised it was not safe
  2. JS in browsers got better [and I got better at it]

It was not safe in as much as it parsed the cookie value once and retained the value. If you were, for instance, using a SPA, Django might update the CSRF token at any point, making your value stale. So instead, I've updated the function to get just one value, and perform parsing on each call.

No, your web framework is not MVC

Whilst it is theoretically possible, I've yet to see a single server-side web framework that is MVC.

"Oh, pshaw!", I hear you say, "But {framework of choice} says it is! So it must be!"

Yeah, and MySQL says it's a good DBMS...

Parsing search strings

We've all had to write a search form at some point. Beyond simple cases, you reach for the big guns, like haystack, et al.

But what about when it's just something simple? What if you want to, for instance, let people search your blog posts?

In django, that can be done simply with:

Registration for Django - the easy way

Every so often (quite frequently, actually) you'll get someone in #django begging for help trying to integrate some app that promises the world ... at least, as far as it concerns user registration and profiles.

Update: A couple of people pointed out the original version would end up requiring the user to enter their email twice. I've now amended the code so the password_reset view's work is now done in the registration CreateView. This makes the view a little more complicated, but the URLs and user workflow much simpler.

The thing is, now that we have custom User models, doing this is easier than ever before - yes, even including email verification.

Serialiser in a hurry

Serialisers are increasingly important now that most web apps are just APIs for the JavaScript to consume.

Serialisers help to reduce your living code objects into simpler types that can be encoded in your serialisation format [typically JSON]. After all, JSON has no date or time types, no classes, etc.

In the Django world, modern REST API libraries separate their Serialiser from the views, and go to great lengths to make them easy to configure, simple to use, and fast. They also support returning your "deflated" data into live code objects.

Using Django's session auth with your SPA

I keep hearing people saying they use Token auth because they think Django's default session-based auth won't work with their Vue/React/whatever Single Page Application (SPA).

This has always baffled me, beyond assuming people are cargo culting something.

Also I've recently had interactions with someone I deeply respect, who also seemed to feel Django's docs on handling authentication with a SPA were lacking.

Sessions aren't better than Cookies

Let the battle begin!

In Django, using the session is just so EASY! There it is on request, behaving like a dict, just being all easy to use.

But sometimes, you're actually better off using cookies.

The simplest API

So, I saw a post recently about Build an API under 30 lines of code using Flask.

I started wondering what it would take to do the same in Django.

The two main tools we're going go use are JsonResponse and ModelForm.

Updating two models in a single post

This comes up a lot in #django ... and the solution is [as many are with Django] much simpler than people assume.

Frequently I see people reach for formsets, in the mistaken conclusion that formsets are for operating on related models. The sad part is that formsets rely on the same functionality that the proper solution relies on, but the seeker does not see it.

Somewhere people get the idea that for a single <form> submission, they can only use a single Form class... but the formset should show that that's not true; it uses multiple forms from the one submission.

Vanilla JS meets Django's CSRF

I was recently helping someone who was trying to learn about building web sites, and was trying to avoid learning too many things at once, so opted to avoid JS libraries for now.

As the discussion progressed, they ran into Django's Cross Site Request Forgery protection which stumped them.

So, as I was about to link them to the part of the docs that shows how to add the CSRF token from the cookie to your headers, I realised it all assumes you're using jQuery.

Wrapping views with decorators

Django provides many decorators for use throughout your project. They can be great time savers, and mastering them can help you DRY your code considerable. However, they often confuse people as to how they work, or how to write their own.

In this post I plan to walk through an example of building up a simple decorator that tests if the user has a specific permission, and if not returning a 403 Forbidden response.

Decorator basics.