'Reads and returns all visible block records for the given course from
the cache.  The cache is initialize with the visible blocks for this
course if no entry currently exists.has no entry for this course,
the cache is updated.
Arguments:
course_key: The course identifier for the desired records'

@classmethod
def bulk_read(cls, course_key):

    prefetched = get_cache(cls.CACHE_NAMESPACE).get(cls._cache_key(course_key))
    if (not prefetched):
        prefetched = cls._initialize_cache(course_key)
    return prefetched
