gistfile1.pyw

from django.conf import settings
from django.core.cache import get_cache
from django.core.cache.backends.base import BaseCache
from django.contrib.sites.models import Site
from django.utils.encoding import smart_str


class CacheClass(BaseCache):
    '''A wrapper around the django cache.

    It adds a prefix to cache keys, useful to avoid key clashes on shared stores
    (e.g. a shared memcache instance). The prefix is omitted if the key starts
    with the current site domain. This is useful when the data are exposed to
    externals clients without depending on any specific key prefix.

    Example configuration in ``settings.py``::

        CACHE_WRAPPED_BACKEND = 'memcached://192.168.1.3:11211?timeout=%(two_days)s' % {'two_days':60*60*24*2}
        CACHE_BACKEND = 'lib.cache.prefixed_cache://community_DEVEL_%(node)s' % {'node':platform.node()}
    '''

    def __init__(self, key_prefix, *args, **kwargs):
        self.key_prefix = smart_str(key_prefix)
        self.wrapped_backend = get_cache(settings.CACHE_WRAPPED_BACKEND)
        super(CacheClass, self).__init__(*args, **kwargs)

    def get_many(self, keys, *args, **kwargs):
        key_prefix = self.key_prefix
        current_domain = Site.objects.get_current().domain
        multi_key = ['%s_%s' % (key_prefix, smart_str(key)) if not
                     key.startswith(current_domain) else key for key in keys]
        prefix_len = len(key_prefix) + 1 # +1 for the '_'
        return dict((k[prefix_len:], v) for k,v in
            self.wrapped_backend.get_many(multi_key, *args, **kwargs).iteritems())

def _cache_wrapper_factory(func_name):
    def wrapper(self, key, *args, **kwds):
        # omit prefix if the key starts with the current site domain.
        if not key.startswith(Site.objects.get_current().domain):
            key = '%s_%s' % (self.key_prefix, smart_str(key))
        return getattr(self.wrapped_backend, func_name)(key, *args, **kwds)
    wrapper.__name__ = func_name
    return wrapper

for name in 'add get set incr delete has_key __contains__'.split():
    assert hasattr(CacheClass, name), 'CacheClass.%s does not exist (typo?)'%name
    setattr(CacheClass, name, _cache_wrapper_factory(name))