I have searched the forum and found some posts favoring using the second-level cache instead of session state when using nHibernate in a web context. But i would like to see some arguments for this approach, as i can not see why it should be better?

The scenario: A typical shoppingbasket needed to be stored in session state for users browsing the product-catalog on a webpage. We have introduced a class called BasketItem having properties NumberOfItems and Item which references the actual Product bought. Price and discount information on the products is used on everypage to calculate the total price and a few other things so i like having it in session, and our products don't change often.

Here comes the catch. A product has a lazyloaded collection which is only needed when showing the contents of the shoppingbasket, but the session is now lost. So i have to reattach the Product objects from HttpSessionState to my current ISession using ISession.Lock(myProduct, LockMode.None).

So my question, is this ISession.Lock call expensive? (it does not look that way looking at logfiles and the actual code) And what would the arguments be in this scenario against this approach and for second-level cache?

If you don't want to lock the object to a new session you could always initialize the collection before you disconnect it from the NHibernate session.

Thanks for your answer!

That was a possibility, but i would like to keep my HttpSession slim, it suits me well that the data is lazyloaded in places used and slim when transferred around.

I would like to hear how people would achieve this using the second-level cache, or other good suggestions

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The main benefit I could see of the second-level cache in most instances is the fact that you don't need to handle your own cache expiry. In your specific instance, since you need to manually control some aspect of the retrieval, I think it would be easier to just use the session context.

I do have a question, though. If you have a collection that only needs to be shown on certain pages, would it maybe be cleaner to not lazy-load the collection? Rather, just load the collection external to the Product.

BasketService.GetBasketItems(parentId) or something like that... then you wouldn't need to worry about manually re-attaching the Product.