@classmethod
def from_db(cls, db, force=False):
    """Make instance from database.

        For performance, this caches the episode types for the database.  The
        `force` parameter can be used to bypass this.

        """
    if force or db not in cls._cache:
        cls._cache[db] = cls._new_from_db(db)
    return cls._cache[db]
