+
−from django.contrib.sessions.backends.base import SessionBase, CreateError
+
−from django.core.cache import cache
+
−
+
−class SessionStore(SessionBase):
+
−    """
+
−    A cache-based session store.
+
−    """
+
−    def __init__(self, session_key=None):
+
−        self._cache = cache
+
−        super(SessionStore, self).__init__(session_key)
+
−
+
−    def load(self):
+
−        session_data = self._cache.get(self.session_key)
+
−        if session_data is not None:
+
−            return session_data
+
−        self.create()
+
−        return {}
+
−
+
−    def create(self):
+
−        # Because a cache can fail silently (e.g. memcache), we don't know if
+
−        # we are failing to create a new session because of a key collision or
+
−        # because the cache is missing. So we try for a (large) number of times
+
−        # and then raise an exception. That's the risk you shoulder if using
+
−        # cache backing.
+
−        for i in xrange(10000):
+
−            self.session_key = self._get_new_session_key()
+
−            try:
+
−                self.save(must_create=True)
+
−            except CreateError:
+
−                continue
+
−            self.modified = True
+
−            return
+
−        raise RuntimeError("Unable to create a new session key.")
+
−
+
−    def save(self, must_create=False):
+
−        if must_create:
+
−            func = self._cache.add
+
−        else:
+
−            func = self._cache.set
+
−        result = func(self.session_key, self._get_session(no_load=must_create),
+
−                self.get_expiry_age())
+
−        if must_create and not result:
+
−            raise CreateError
+
−
+
−    def exists(self, session_key):
+
−        if self._cache.get(session_key):
+
−            return True
+
−        return False
+
−
+
−    def delete(self, session_key=None):
+
−        if session_key is None:
+
−            if self._session_key is None:
+
−                return
+
−            session_key = self._session_key
+
−        self._cache.delete(session_key)
+
−