listy-django-cache

listy-django-cache is a deterministic caching mechanism for Django projects. It will attempt to keep the cache in-sync with the database by updating during changes instead of relying on timeouts. As implied by the name, Listy supports looking up lists of objects.

Install

 pip install listy-django-cache

Usage

Using Listy is as simple as replacing the default model manager with a CachingManager and providing it with the list of keys that you will want to query with.

In this contrived example, I can look up based on pk, just the follower, or both the follower and followee:

import listy

class Follow(models.Model):
 # Configure this cache to support lookup by 'pk' or 'follower'
 objects = listy.CachingManager([('pk',), ('follower',), ('follower', 'followee')])
 created = models.DateTimeField(auto_now_add=True)
 follower = models.ForeignKey('User', related_name='follows')
 followee = models.ForeignKey('User', related_name='followers')

# Follow someone
Follow.cache.add(follower=me, followee=you)

# Unfollow someone
Follow.cache.delete(follower=me, followee=you)

# Get the users I follow
Follow.cache.get(follower=me)

# Get whether I follow you
Follow.cache.get(follower=me, follower=you)

# Get the counts for the users I follow
from datetime import date, timedelta
from dateutil.rrule import rrule, DAILY, WEEKLY, MONTHLY, YEARLY
start, end = date.today() - timedelta(days=100), date.today()
Follow.cache.daily_counts(created=rrule(DAILY, dtstart=start, until=end))

You can see a complete set of examples in test_django_app/caching/tests.py.

Arguments to CachingManager:

- caches -- a list of tuples describing the fields that should be keys into the cache
- soft_delete_field -- the name of the delete field that can be used to delete objects without actually removing them from the database if this feature is supported by the model (default None)
- deleted_timestamp_field -- the name of the field which should be set to a datetime when deleting an object (default None)
- enabled_field -- the name of the field which defines whether an object is enabled or not, this is treated like a delete that cannot be undone under normal circumstances (default None)
- timestamp_field -- the name of the field that hold the timestamp to be used for the counters (default None)
- disable_cache -- turn off caching, can be used for debugging (default False)
- address -- a function that returns the address of the memcache (default 127.0.0.1:11211)
- filter_out_soft_deletes -- treat soft deletes as true deletes, filter them out when returning lists (default True)

The list of tuples defined by the caches argument is the heart of this caching mechanism. Through it we define what lists of objects we want cached and updated, and how we will access those lists.

Features:

• Very easy to use
• Deterministic
• Fast access to lists of things
• Packs data into compact form (most small records go from about 1k down to 10s of bytes)
• On-demand deserialization
• Use of memcache's prepend command for fast adds
• Keeps track of total, yearly, monthly, weekly, and daily counts for each cached list
• Optional per-request object registry
• Optional support for soft deletes

Requirements:

• Python
• Django