'Return the active data entry, if any, otherwise None'

@classmethod
def current(cls, entity_id):

    cached = cache.get(cls.cache_key_name(entity_id))
    if (cached is not None):
        return cached
    try:
        current = cls.objects.filter(entity_id=entity_id).order_by('-fetched_at')[0]
    except IndexError:
        current = None
    cache.set(cls.cache_key_name(entity_id), current, cls.cache_timeout)
    return current
