"A slight increase in serialization time in my performance tests. De-serialization is still as fast as before"
-> Caused by treating collections as non native objects, now the whole collections are serialized, not only simulated by limited native objects
"Query<T>() is now AsQuerayble<T> which actually makes more sense. (so I had to update my code a bit)."
-> old Query<T>() is removed, new Query<T>() is the factory method for creating query, AsQueryable<T> is IQueryable correspondence to SODA Query<T>().Execute<T>()
Whole Query API is changed, so changes needs to be done on client side too (if queries were used often). But that's the final Query API for the NDatabase, which will be extended in the future. (Breaking change)
Additionally, db layer (binary) is changed too, so the way how to treat collections. I will prepare converter between 2.0-2.3 -> new release.
"Checked the SODA site very quickly but finding some documentation was not straight forward."
-> Agree, but during the release the actual documentation will be delivered/updated too :)
"Will NDatabase provide an easy mechanism to go from/to relational databases in the future or at least provide a language translator from SQL to LINQ? (or is that what SODA is meant for?)"
-> For the direction 'to relational databases', the xml import/export will be prepared, the further processing of that (or directly from NDatabase) to any relational db depends from users.
-> For the direction 'from relational databases' in terms of moving data, that will be definitely researched. Ticket for that: http://ndatabase.codeplex.com/workitem/891
-> more info about SODA http://sodaquery.sourceforge.net/, query similar to what you have there: http://community.versant.com/documentation/reference/db4o-7.12/java/reference/html/content/object_lifecycle/querying/soda_query/soda_query_api.html