As far as I know there is no elegant way to do that with CActiveRecord but the question is: Why do you need that? If you want to be sure your book is always in cache you could set the first parameter to an insane number. If you need to invalidate the cache (like when a book was updated etc.) you can use this extension as a cache dependency: http://www.yiiframework.com/extension/flushable
If - for some reason - you really need to know if the row is in the cache or not you will have to know the cache key. Yii generates a pretty long one to avoid collisions but nobody prevents you from using your own like