NHibernate not finding named query result sets in 2nd level cache

Question

I have a simple unit test where I execute the same NHibernate named query 2 times (different session each time) with the identical parameter. It's a simple int parameter, and since my query is a named query I assume these 2 calls are identical and the results should be cached.

In fact, I can see in my log that the results ARE being cached, but with different keys. So, my 2nd query results are never found in cache.

here's a snip from my log (note how the keys are different):

(first query) DEBUG NHibernate.Caches.SysCache2.SysCacheRegion [(null)] <(null)> - adding new data: key= [snipped]... parameters: ['809']; named parameters: {}@743460424 & value=System.Collections.Generic.List`1[System.Object]

(second query) DEBUG NHibernate.Caches.SysCache2.SysCacheRegion [(null)] <(null)> - adding new data: key=[snipped]... parameters: ['809']; named parameters: {}@704749285 & value=System.Collections.Generic.List`1[System.Object]

I have NHibernate set up to use the query cache. And I have these queries set to cacheable=true. Don't know where else to look. Anyone have any suggestions?

Thanks
-Mike

Answer 1

Okay - i figured this out. I was executing my named query using the following syntax:

IQuery q = session.GetNamedQuery("MyQuery")
                .SetResultTransformer(Transformers.AliasToBean(typeof(MyDTO)))
                .SetCacheable(true)
                .SetCacheRegion("MyCacheRegion");

( which, I might add, is EXACTLY how the NHibernate docs tell you how to do it.. but I digress ;) )

If you use create a new AliasToBean Transformer for every query, then each query object (which is the key to the cache) will be unique and you will never get a cache hit. So, in short, if you do it like the nhib docs say then caching wont work.

Instead, create your transformer one time in a static member var and then use that for your query, and caching will work - like this:

private static IResultTransformer myTransformer = Transformers.AliasToBean(typeof(MyDTO))

...

IQuery q = session.GetNamedQuery("MyQuery")
                    .SetResultTransformer(myTransformer)
                    .SetCacheable(true)
                    .SetCacheRegion("MyCacheRegion");