What does the ContentType application do in Django?

Did you know that Django keeps track of each of the models you create for your project in a model called ContentType? Read on to learn about it.

Sorry for taking so long to write! I’ve been busy moving the frontend of my blog to Frontity, a React framework for Wordpress, and also moving to a new apartment. Maybe I’ll talk a bit about Frontity in a future post. For now let’s get on with it.

Before we start, if you have no idea what Django is for, visit my post where I talk about (why you should use django)[/en/why-should-you-use-django-framework/] If you’ve used Django before, let’s move on.

ContentType and models

ContentTypes is a special Django model that registers each of the models that exist within our application, both those that we create and those that are installed by default.

What is ContentType used for?

ContentType serves to relate models with other models, as if it were a foreign key, but with the advantage that the type of model with which we relate it can be different for each table entry.

Imagine a simple social network, where we have different types of content; a template for videos, a template for images and a template for text. ContentType allows us to create a model that references any of our three models in a simple way, even if they’re completely different models.

How to use ContentType?

To exemplify how ContentType works, let’s create a django project, with a model:

First let’s create a virtual environment with Pipenv, the virtual environment manager . Or you can also use pip.

pipenv shell

Once in our virtual environment, let’s install Django

pip install django

Let’s create a project:

django-admin startproject videogameStore
cd videogameStore

Now we will create an app for our application.

django-admin startapp videogame
cd videogame

Once we have our application, we will have to create a template, and, as I already mentioned, Django will automatically register that template in its ContentType application.

The first thing we will do is open our models.py file and edit the content of the file

from django.db import models

# Create your models here.

class Videogame(models.Model):
    name = models.CharField(max_length=256)
    created = models.DateTimeField(auto_now_add=True)
    modified = models.DateTimeField(auto_now=True)

We must remember to add our newly created app to our settings.py file.

INSTALLED_APPS = [
    ...,
    'videogame'
]

We create the migrations and execute them. Pay attention to how to create migrations for the ContentTypes application in Django.

python3 manage.py makemigrations
Migrations for 'videogame':
  videogame/migrations/0001_initial.py
    - Create model Videogame
python3 manage.py migrate
Operations to perform:
  Apply all migrations: admin, auth, contenttypes, sessions, videogame
Running migrations:
  Applying contenttypes.0001_initial... OK
  Applying auth.0001_initial... OK
...

Now we will have a model registered in ContentType. Let’s check it directly from Django’s shell.

python manage.py shell

Once in the terminal, let’s import the ContentType model.

How to get models from ContentType in Django?

Just like any other model, we can use your ORM to get the data from the models.

Each object of the ContentType model will have a property called app_label, and another model, which are the name of the application and the name of the model, respectively.

from django.contrib.contenttypes.models import ContentType
ContentType.objects.get(app_label='videogame', model="videogame")
<ContentType: videogame | videogame>

If you prefer, you can also access the ContentType instance directly from the model using the get_for_model method.

from videogame.models import Videogame
ContentType.objects.get_for_model(Videogame)
<ContentType: videogame | videogame>

Other models stored in Django ContentType

As you know, each table entry has a unique identifier, the id, see what happens if we access the id of the instance we just created.

ContentType.objects.get(app_label='videogame', model="videogame").id
7

Yes, as you may have already guessed, there are more models registered in the ContentType app. Let’s find out what they are.

>>> ContentType.objects.get(id=1)
<ContentType: admin | log entry>
ContentType.objects.get(id=2)
<ContentType: auth | permission>
ContentType.objects.get(id=3)
<ContentType: auth | group>
ContentType.objects.get(id=4)
<ContentType: auth | user>

As I already mentioned, each of the default installed apps has its respective models.

If you want to go deeper into the subject please check the official Django documentation