SetCacheable throws IndexOutOfBoundsException - nhibernate

Question

I have following query in NHibernate where the result is a list of DTO's, not entities:
var result = query
//.SetCacheable(true)
.SetResultTransformer(new MyDTOTransformer())
.List<DTO>();
This works with SetCacheable in comment but it throws an IndexOutOfBoundsException when I set SetCacheable to true.
This is the stacktrace:
at NHibernate.Type.TypeFactory.Disassemble(Object[] row, ICacheAssembler[] types, Boolean[] nonCacheable, ISessionImplementor session, Object owner)
at NHibernate.Cache.StandardQueryCache.Put(QueryKey key, ICacheAssembler[] returnTypes, IList result, Boolean isNaturalKeyLookup, ISessionImplementor session)
at NHibernate.Loader.Loader.PutResultInQueryCache(ISessionImplementor session, QueryParameters queryParameters, IType[] resultTypes, IQueryCache queryCache, QueryKey key, IList result)
at NHibernate.Loader.Loader.ListUsingQueryCache(ISessionImplementor session, QueryParameters queryParameters, ISet`1 querySpaces, IType[] resultTypes)
at NHibernate.Loader.Loader.List(ISessionImplementor session, QueryParameters queryParameters, ISet`1 querySpaces, IType[] resultTypes)
at NHibernate.Loader.Custom.CustomLoader.List(ISessionImplementor session, QueryParameters queryParameters)
at NHibernate.Impl.SessionImpl.ListCustomQuery(ICustomQuery customQuery, QueryParameters queryParameters, IList results)
at NHibernate.Impl.SessionImpl.List(NativeSQLQuerySpecification spec, QueryParameters queryParameters, IList results)
at NHibernate.Impl.SessionImpl.List[T](NativeSQLQuerySpecification spec, QueryParameters queryParameters)
at NHibernate.Impl.SqlQueryImpl.List[T]()
at ...
Can anyone help me and say how I can fix this (or even if this is supported in NHibernate)?
I'm currently using NHibernate-version 2.1.0.4000.
Thank you,
Jelle

Answer 1

I may be mistaken, but I think that the query cache relies on the second level cache being enabled. To be honest, I wonder if it would be all that useful without entity caching in the second level cache, because all the it stores is a list of ID's associated with a given query / parameter combination (you'd still need to go to the database to actually get the objects, and in some situations this could lead to 1 query per object).
This is one of the better posts on caching in nhibernate that I've seen, and it seems to suggest towards the end that you can only cache queries in the second level cache

Answer 2

I had this same exception, and it's fixed now. Yesterday when I used a second cache by setting SetCacheable for my entity, an IndexOutOfBoundsException occurred.
I Googled for it and found a blog that mentioned it may be a problem with my Customer Entity. I tried query.setCacheable(true);, and added query.setCacheMode(CacheMode.GET); and it worked! Give this solution a try.

Answer 3

I think you just need to "declare" your columns that you are returning from your DTO, by using AddScalar. Without the AddScalar lines below (one for each of the columns in your result set) there is no column definition meta-data which the second-level cache code needs (and thus the index out of bounds exception)
Just use AddScalar to list all of your columns being returned and I'll bet it works.
var result = query
//.SetCacheable(true)
.AddScalar("yourfirstcolumn",NHibernateUtil.Int32)
.AddScalar("yoursecondcolumn",NHibernateUtil.String)
.SetResultTransformer(new MyDTOTransformer())
.List<DTO>();