A way to globally disable writes to your database. This works by
inserting a cursor wrapper between Django's CursorWrapper and the
database connection's cursor wrapper.
The library is hosted on PyPi, so you can grab it there with:
pip install django-db-readonly
Then add readonly to your INSTALLED_APPS.:
INSTALLED_APPS = (
# ...
'readonly',
# ...
)
You need to add this line to your settings.py to make the database read-only:
# Set to False to allow writes SITE_READ_ONLY = True
When you do this, any write action to your databases will generate an
exception. You should catch this exception and deal with it somehow. Or
let Django display an error 500
page.
The exception you will want to catch is
readonly.exceptions.DatabaseWriteDenied which inherits from
django.db.utils.DatabaseError.
There is also a middleware class that will handle the exceptions and
attempt to handle them as explained below. To enable the middleware, add the following line to your
settings.py:
MIDDLEWARE_CLASSES = (
# ...
'readonly.middleware.DatabaseReadOnlyMiddleware',
# ...
)
This will then catch DatabaseWriteDenied exceptions. If the request is a POST request, we
will redirect the user to the same URL, but as a GET request. If the
request is not a POST (ie. a GET), we will just display a
HttpResponse with text telling the user the site is in read-only
mode.
In addition, the middleware class can add an error-type message using
the django.contrib.messages module. Add:
# Enable DB_READ_ONLY_MIDDLEWARE_MESSAGE = True
to your settings.py and then on POST requests that generate a
DatabaseWriteDenied exception, we will add an error message
informing the user that the site is in read-only mode.
For additional messaging, there is a context processor that adds
SITE_READ_ONLY into the context. Add the following line in your
settings.py:
TEMPLATE_CONTEXT_PROCESSORS = (
# ...
'readonly.context_processors.readonly',
# ...
)
And use it as you would any boolean in the template, e.g.
{% if SITE_READ_ONLY %} We're down for maintenance. {% endif %}
There aren't any tests included, yet. Run it at your own risk.
This will work with Django Debug Toolbar. In fact, I was inspired by DDT's sql panel when writing this app.
However, in order for both DDT and django-db-readonly to work, you
need to make sure that you have readonly before debug_toolbar in
your INSTALLED_APPS. Otherwise, you are responsible for debugging
what is going on. Of course, I'm not sure why you'd be running DDT in
production and running django-db-readonly in development, but whatever,
I'm not you.
More generally, if you have any other apps that modifies either
django.db.backends.util.CursorWrapper or
django.db.backends.util.CursorDebugWrapper, you need to make sure
that readonly is placed before of those apps in
INSTALLED_APPS.
How does this do what it does? Well, django-db-readonly sits between
Django's own cursor wrapper at django.db.backends.util.CursorWrapper
and the database specific cursor at
django.db.backends.*.base.*CursorWrapper. It overrides two specific
methods: execute and executemany. If the site is in read-only
mode, then the SQL is examined to see if it contains any write actions
(defined in readonly.ReadOnlyCursorWrapper.SQL_WRITE_BLACKLIST). If
a write is detected, an exception is raised.
Uses the MIT license.