Contenttypes Framework

Created at: 2025-03-27

What is it?

A generic interface for working with Django models.

The ContentType model

The ContentType model is at the core of the framework. It has the columns

• app_label: str
• model: str
• name: str (verbose name obtained from the model's verbose_name attribute)

Rows are injected into that table whenever new models are installed.

There are methods on this model for both finding the model for a row, and for getting a row for a model.

• ContentType.get_object_for_this_type(...get() args...) Takes a set of valid lookup arguments for the model the ContentType represents, and does a get() lookup on that model, returning the corresponding object from the underlying model.
• ContentType.model_class() get the model for a row.

from django.contrib.contenttypes.models import ContentType
user_type = ContentType.objects.get(app_label="auth", model="user")
user_type
# <ContentType: user>

user_type.model_class()
# <class 'django.contrib.auth.models.User'>
user_type.get_object_for_this_type(username="Guido")
# <User: Guido>

Generic Relations

ContentType is also used for Generic Relations.

You can relate another model to ContentType as a way of tying instances of it to particular model classes, and use these methods to get access to those model classes.

from django.contrib.contenttypes.fields import GenericForeignKey
from django.contrib.contenttypes.models import ContentType
from django.db import models


class TaggedItem(models.Model):
    tag = models.SlugField()
    # STEP 1: You need a foreign key to the ContentType model.
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
    # STEP 2: A field that can store the type of "id" to any of the desired
    # generic models you want to link to.
    # NOTE: you can't support multiple objects with different id types under
    # this strategy. Unless you use something like a varchar that can be
    # coerced to different types.
    object_id = models.PositiveIntegerField()
    # STEP 3: Give the model a GenericForeignKey, and pass it the names of the
    # two fields described above. If these fields are named “content_type” and
    # “object_id”, you can omit this – those are the default field names.
    # NOTE: this field is not "filterable" so the following will fail:
    # TaggedItem.objects.filter(content_object=guido)
    content_object = GenericForeignKey("content_type", "object_id")

    def __str__(self):
        return self.tag

    class Meta:
        indexes = [
            # These fields are not automatically index, so create your own.
            models.Index(fields=["content_type", "object_id"]),
        ]

Say you want to get the object of that content type:

from django.contrib.auth.models import User
guido = User.objects.get(username="Guido")
t = TaggedItem(content_object=guido, tag="bdfl")
t.save()
t.content_object
# <User: Guido>

guido.delete()
t.content_object  # returns None

You can also use a reverse relationship:

from django.contrib.contenttypes.fields import GenericRelation
from django.db import models


class Bookmark(models.Model):
    url = models.URLField()
    tags = GenericRelation(TaggedItem)

b = Bookmark(url="https://www.djangoproject.com/")
b.save()
t1 = TaggedItem(content_object=b, tag="django")
t1.save()
t2 = TaggedItem(content_object=b, tag="python")
t2.save()
b.tags.all()

Resources

Official docs: https://docs.djangoproject.com/en/5.1/ref/contrib/contenttypes/

Blog post describing why you should not use this: https://lukeplant.me.uk/blog/posts/avoid-django-genericforeignkey/