Filter collections with Django
django-oso library can enforce policies over Django models. This allows
policies to control access to collections of objects without needing to
authorize each object individually.
The Oso Django integration is available on
PyPI and can be installed using
$ pip install django-oso
The easiest way to prepare your existing Django models for use in a list
filtering policy is to have them inherit from
django_oso.models.AuthorizedModel(), a thin wrapper around
django.models.Model that calls
under the hood to return Django
QuerySets with authorization filters applied.
The policies you write will largely look the same with or without the list filtering feature, and the Oso engine will follow similar evaluation paths.
In the list filtering case, Oso consults the policy to build up a list of conditions that must be met in order for a model to be authorized. These conditions are translated into Django ORM filters and applied to the query before retrieving objects from the database.
Let’s look at an example usage of this library. Our example is a social media
app that allows users to view posts. There is a
User model and a
from django.db import models from django.contrib.auth.models import AbstractUser from django_oso.models import AuthorizedModel class User(AbstractUser): is_admin = models.BooleanField(default=False) manager = models.ForeignKey( "self", null=True, related_name="direct_reports", on_delete=models.CASCADE ) class Post(AuthorizedModel): contents = models.CharField(max_length=255) AccessLevelType = models.TextChoices("AccessLevelType", "public private") access_level = models.CharField( choices=AccessLevelType.choices, max_length=7, default="private" ) creator = models.ForeignKey(User, on_delete=models.CASCADE) class Meta: app_label = "app"
We want to enforce the following authorization scheme for posts:
- Anyone is allowed to
GETany public post.
- A user is allowed to
GETtheir own private posts.
- A user is allowed to
GETprivate posts made by users they manage (defined through the
The corresponding policy looks as follows:
# Anyone may view public posts. allow(_: app::User, "GET", post: app::Post) if post.access_level = "public"; # Users may view their own private posts. allow(user: app::User, "GET", post: app::Post) if post.access_level = "private" and post.creator = user; # Users may view private posts created by users who they manage. allow(user: app::User, "GET", post: app::Post) if post.access_level = "private" and post.creator in user.direct_reports.all();
Trying it out
If you want to follow along, clone the Oso repository from
into it and then into the
make setup to install dependencies (primarily Django and
django-oso) and seed the database.
The database now contains a set of four posts made by two users:
manager = User(username="manager") user = User(username="user", manager=manager) Post(contents="public user post", access_level="public", creator=user) Post(contents="private user post", access_level="private", creator=user) Post(contents="public manager post", access_level="public", creator=manager) Post(contents="private manager post", access_level="private", creator=manager)
Once everything is set up, run
python example/manage.py runserver to start
the Django app. We can now use cURL to interact with the application.
A guest user may view public posts:
$ curl localhost:8000/posts 1 - @user - public - public user post 3 - @manager - public - public manager post
A non-manager may view public posts and their own private posts:
$ curl --user user:user localhost:8000/posts 1 - @user - public - public user post 2 - @user - private - private user post 3 - @manager - public - public manager post
A manager may view public posts, their own private posts, and private posts of their direct reports:
$ curl --user manager:manager localhost:8000/posts 1 - @user - public - public user post 2 - @user - private - private user post 3 - @manager - public - public manager post 4 - @manager - private - private manager post
How it works
QuerySets containing authorized models are automatically filtered using
constraints derived from the policy.
For example, the above policy has the following rule:
allow(user: app::User, "GET", post: app::Post) if post.access_level = "private" and post.creator = user;
When determining which
User(id=2) is authorized to see,
django-oso adapter converts the constraints on Post expressed in this
rule into a Django
(AND: ('access_level', 'private'), ('creator__pk', 2))
When composed with filters generated from the other rules, the
scoped down to include only authorized objects. The result is the following SQL
statement, with the highlighted clause corresponding to the above filter:
SELECT "app_post"."id", "app_post"."contents", "app_post"."access_level", "app_post"."creator_id" FROM "app_post" WHERE "app_post"."id" IN ( SELECT DISTINCT U0."id" FROM "app_post" U0 WHERE ( U0."access_level" = 'public' OR (U0."access_level" = 'private' AND U0."creator_id" = 2)));
There are some operators and features that do not currently work with the Django adapter when used anywhere in the policy:
- Rules that rely on ordered execution based on class inheritance.
Some operations cannot be performed on authorized models in rules used with the Django adapter. These operations can still be used on regular Django models or Python objects:
- Application method calls.
- Arithmetic operators.
Connect with us on Slack
If you have any questions, or just want to talk something through, jump into Slack. An Oso engineer or one of the thousands of developers in the growing community will be happy to help.