def get(self, *args, **kwargs):
"""
Checks the cache to see if there's a cached entry for this pk. If not, fetches
using super then stores the result in cache.
Most of the logic here was gathered from a careful reading of
``django.db.models.sql.query.add_filter``
"""
if self.query.where:
# If there is any other ``where`` filter on this QuerySet just call
# super. There will be a where clause if this QuerySet has already
# been filtered/cloned.
return super(CachingQuerySet, self).get(*args, **kwargs)
# Punt on anything more complicated than get by pk/id only...
if len(kwargs) == 1:
k = kwargs.keys()[0]
if k in ('pk', 'pk__exact', '%s' % self.model._meta.pk.attname,
'%s__exact' % self.model._meta.pk.attname):
obj = cache.get(self.model._cache_key(pk=kwargs.values()[0]))
if obj is not None:
obj.from_cache = True
return obj
obj = super(CachingQuerySet, self).get(*args, **kwargs)
cache.set(obj.cache_key,obj)
return obj
def _invalidate_cache(self, instance):
"""
Explicitly set a None value instead of just deleting so we don't have any race
conditions where:
Thread 1 -> Cache miss, get object from DB
Thread 2 -> Object saved, deleted from cache
Thread 1 -> Store (stale) object fetched from DB in cache
Five second should be more than enough time to prevent this from happening for
a web app.
"""
cache.set(instance.cache_key, None)
def post_save_cache(sender,instance,**kwargs):
cache.set(instance.cache_key,instance)
def invalidate_cache(obj, field):
cache.set(obj._get_cache_key(field=field), None, 5)
