Skip to content
This repository

HTTPS clone URL

Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP

Automated caching and invalidation for the Django ORM

branch: master

Fetching latest commit…

Octocat-spinner-32-eaf2f5

Cannot retrieve the latest commit at this time

Octocat-spinner-32 cachebot
Octocat-spinner-32 .gitignore
Octocat-spinner-32 LICENSE
Octocat-spinner-32 MANIFEST.in
Octocat-spinner-32 README.rst
Octocat-spinner-32 setup.py
README.rst

Django-cachebot

Django-cachebot provides automated caching and invalidation for the Django ORM.

Installation

  1. easy_install django-cachebot or pip install django-cachebot

  2. Add cachebot to your INSTALLED_APPS

  3. Set a cache backend to one of the backends in cachebots.backends, for instance:

    CACHES = {
        'default': {
            'BACKEND': 'cachebot.backends.memcached.MemcachedCache',
            'LOCATION': '127.0.0.1:11211',
        }
    }
    

Current supported backends are:

cachebot.backends.dummy.DummyCache
cachebot.backends.memcached.MemcachedCache
cachebot.backends.memcached.PyLibMCCache
  1. If you want to add caching to a model, the model's manager needs to be CacheBotManager or a subclass of it, e.g:

    from django.db import models
    from cachebot.managers import CacheBotManager
    
    class Author(models.Model):
        name = models.CharField(max_length=50)
        objects = CacheBotManager()
    
    class BookManager(CacheBotManager):
    
        def for_author(self, name):
            return self.filter(author__name=name)
    
    class Book(models.Model):
        title = models.CharField(max_length=50)
        author = models.ForeignKey(Author)
        objects = BookManager()
    

Usage

By default, all get queries for CacheBotManager will be cached:

photo = Photo.objects.get(user=user)

If you don't want this behavior, call CacheBotManager(cache_get=False) when defining the manager, or to change this globally set CACHEBOT_CACHE_GET=False in settings.


For more complex queries, suppose you had a query that looked like this and you wanted to cache it:

Photo.objects.filter(user=user, status=2)

Just add .cache() to the queryset chain like so:

Photo.objects.cache().filter(user=user, status=2)

This query will get invalidated if any of the following conditions are met:

1. One of the objects returned by the query is altered.
2. The user is altered.
3. A Photo is modified and has status = 2.
4. A Photo is modified and has user = user.

This invalidation criteria is probably too cautious, because we don't want to invalidate this cache every time a Photo with status = 2 is saved. To fine tune the invalidation criteria, we can specify to only invalidate on certain fields. For example:

Photo.objects.cache('user').filter(user=user, status=2)

This query will get invalidated if any of the following conditions are met:

1. One of the objects returned by the query is altered.
2. The user is altered.
3. A Photo is modified and has user = user.

django-cachebot can also handle select_related, forward relations, and reverse relations, ie:

Photo.objects.select_related().cache('user').filter(user__username="david", status=2)

Photo.objects.cache('user').filter(user__username="david", status=2)

Photo.objects.cache('message__sender').filter(message__sender=user, status=2)

Settings

  • CACHEBOT_CACHE_GET
    • default: True
    • If set to True, CacheBotManager will be called with cache_get=True by default.
  • CACHEBOT_TABLE_BLACKLIST
    • default: ('django_session', 'django_content_type', 'south_migrationhistory')
    • A list of tables that cachebot should ignore.

Caveats (Important!)

  1. Adding/Removing objects with a ManyRelatedManager will not automatically invalidate. You'll need to manually invalidate these queries like so:

    from cachebot.signals import invalidate_object
    
    user.friends.add(friend)
    invalidate_object(user)
    invalidate_object(friend)
    
  2. count() queries will not get cached.

  3. If you're invalidating on a field that is in a range or exclude query, these queries will get invalidated when anything in the table changes. For example the following would get invalidated when anything on the User table changed:

    Photo.objects.cache('user').filter(user__in=users, status=2)
    
    Photo.objects.cache('user').exclude(user=user, status=2)
    
  4. You should probably use a tool like django-memcache-status to check on the status of your cache. If memcache overfills and starts dropping keys, it's possible that your queries might not get invalidated.

  5. .values_list() doesn't cache yet. You should do something like this instead:

    [photo['id'] for photo in Photo.objects.cache('user').filter(user=user).values('id')]
    

Dependencies

  • Django 1.3

If you use Django 1.2, you can use django-cachebot version 0.3.1

Something went wrong with that request. Please try again.