return self.get_value(createfunc=lambda:

                                  list(Query.__iter__(self)))

        else:

            return Query.__iter__(self)

    def invalidate(self):

        """Invalidate the value represented by this Query."""

        cache, cache_key = _get_cache_parameters(self)

        cache.remove(cache_key)

    def get_value(self, merge=True, createfunc=None):

        """Return the value from the cache for this query.

        Raise KeyError if no value present and no

        createfunc specified.

        """

        cache, cache_key = _get_cache_parameters(self)

        ret = cache.get_value(cache_key, createfunc=createfunc)

        if merge:

            ret = self.merge_result(ret, load=False)

        return ret

def query_callable(manager, query_cls=CachingQuery):

    def query(*arg, **kw):

        return query_cls(manager, *arg, **kw)

    return query

def get_cache_region(name, region):

    if region not in beaker.cache.cache_regions:

        raise BeakerException('Cache region `%s` not configured '

            'Check if proper cache settings are in the .ini files' % region)

    kw = beaker.cache.cache_regions[region]

    return beaker.cache.Cache._get_cache(name, kw)

def _get_cache_parameters(query):

    """For a query with cache_region and cache_namespace configured,

    return the corresponding Cache instance and cache key, based

    on this query's current criterion and parameter values.

    """

    if not hasattr(query, '_cache_parameters'):

        raise ValueError("This Query does not have caching "

                         "parameters configured.")