A generic cache manager

A generic cache manager.

from django.db.models.query import QuerySet
from django.core.cache import cache
from django.db import models
import random

# douglas goodwin 4/2010
# eculver's code with a couple of fixes and instructions
#
# maybe not the nest way to do it but...
#
# paste this into a file called cachemanager.py on your django path
# in your models.py file:
#
# from cachemanager import CacheManager
#
# then:
# Class BlahBlah(models.Model):
# ...
#    objects = CacheManager()
#
# then, in your views.py the usual business:
# allblahblah = BlahBlah.objects.all()

class CacheManager(models.Manager):
	
	def _test_mymodel(obj, *args):
		''' Checks to see if the current object is up-to-date with it's model.
			Returns True if it is, otherwise False.
			Used to tell if an object fetched from cache is fresh.
			NOTE: changed method name to avoid namespace collision (DGOODWIN 7/2010)
			NOTE: Added *args to trap instances where too many args have been passed (DGOODWIN 7/2010)
		'''
		# Duct tape way to make the conditionals work
		if len(args) > 0:
			return False
		if obj is None:
			return False
		# Compares the object to a blank version of the model
		res = dir(obj)==dir(obj.__class__())
		return res

	def _get_model_string(self):
		''' Return the correct string for a given model. '''
		return self.model.__name__.lower()
	
	def _get_generator_id(self):
		''' Return the generator id for a given model.
			This is used for getting and invalidating collections.
			<model_name>-generator_id -> generator_id
			<model_name>-<generator_id> -> <collection>
			
			On save, save new generator id, auto-invalidates all collections.
			Generator id is just a random 5-digit number.
		'''
		key = "%s-generator_id" % self._get_model_string()
		generator_id = cache.get(key)
		
		if not generator_id:
			cache.set(key, int(random.random() * 100000), 60 * 60 * 48) # 48 hours.
			
		return generator_id
	
	def get(self, **kwargs):
		''' Return the object by id. Sets it into cache. If no object is
			found, returns None.
		'''
		key = self._get_model_string()
		for k,v in kwargs.iteritems():
			key = "%s:%s:%s" % (key, k, v)
			
		object = cache.get(key)

		if not object or not self._test_mymodel(object):
			try:
				object = super(CacheManager, self).get(**kwargs)
				cache.set(key, object, 60 * 60 * 24)
			except self.model.DoesNotExist:
				object = None

		return object

	def filter(self, **kwargs):
		''' Try to get a bunch of objects from cache.
			Uses generator_id and signals to make sure that it's getting the 
			most up to date collection. On save, a new generator_id is 
			generated.
		'''
		key = "%s-%s" % (self._get_model_string(), self._get_generator_id())
		for k,v in kwargs.iteritems():
			key = "%s:%s:%s" % (key, k, v)

		objects = cache.get(key)

		if not objects:
			objects = super(CacheManager, self).filter(**kwargs)
			cache.set(key, objects)

		return objects
		
	def all(self):
		''' Try to get all objects from cache. '''
		key = "%s:all" % self._get_model_string()
		objects = cache.get(key)
		
		if not objects:
			objects = super(CacheManager, self).all()
			cache.set(key, objects)
		
		return objects