django-sans-db

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 %}