django-sans-db 1.2.0

Tools to limit database access in parts of your Django codebase

Django sans DB

Tools for limiting access to the database in parts of your Django code.

Installation

pip install django-sans-db

If you wish to use the {% sansdb %} template tag, you will need to add "sans_db" to your INSTALLED_APPS.

Usage

Context manager

You can block access to your database for a section of your code using block_db:

from sans_db.context_managers import block_db

User.objects.create(...)  # Works outside of block_db()
with block_db():
    User.objects.get()  # Raises DatabaseAccessBlocked

If you have multiple entries in your Django DATABASES setting, then block_db will default to blocking all of them.

If you wish to block access to a subset of your databases, pass a list of their aliases (the keys in the DATABASES dictionary).

from sans_db.context_managers import block_db

with block_db(databases=["replica"]):
    User.objects.using("primary").create(...)  # This DB isn't blocked.
    User.objects.using("replica").get()  # Raises DatabaseAccessBlocked

Decorator

You can decorate functions and methods with block_db to block database access in them. Eg:

from sans_db.context_managers import block_db

class MyClass:
    def allowed(self):
        User.objects.create(...)  # Works outside of block_db()

    @block_db()
    def not_allowed(self):
        User.objects.create(...)  # Raises DatabaseAccessBlocked

Template backend

You can block access to the database when rendering Django templates with our custom template backend.

Note: Currently, only Django templates are supported.

You can block database access in all of your templates by setting your templates backend to "sans_db.template_backends.django_sans_db.DjangoTemplatesSansDB"

For example:

# settings.py

TEMPLATES = [
    {
        "BACKEND": "sans_db.template_backends.django_sans_db.DjangoTemplatesSansDB",
        "APP_DIRS": True,
        "OPTIONS": {...},
    },
]

Attempts to query the database will now cause a sans_db.exceptions.DatabaseAccessBlocked to be raised.

Please refer to Django's docs on support for template engines for details on how to set this up as a secondary template renderer.

Template tag

You can block DB access in a portion of your template by wrapping it with the {% sansdb %} template tag.

The template tag accepts database aliases as either strings, or variables. If passed as a variable, either strings or iterables of strings are accepted. If no aliases are passed, all databases will be blocked.

Note: DatabaseAccessBlocked is raised when an attempt is made to access the DB.

To block all databases:

{% load sansdb %}
{% sansdb %}
    {# ... #}
{% endsansdb %}

To block a list of databases named in the template:

{% load sansdb %}
{% sansdb "second_db" "third_db" %}
    {# ... #}
{% endsansdb %}

To block a list of databases from a context variable:

{% load sansdb %}
{% sansdb databases %}
    {# ... #}
{% endsansdb %}