Can first level cache be used with ICriteria or other APIs?

Question

In NHibernate you can easily benefit from first level cache when using Load or Get methods. But what about ICriteria, HQL, Linq-to-NHibernate and QueryOver? Do they use first level cache too?

Answer 1

They use it for returning entities, but the queries go straight to the db unless you use the second level cache.

Consider this:

var fooUsingGet = session.Get<Foo>(fooId);
var fooQueryById = session.Query<Foo>().Single(f => f.Id == fooId);

Two queries are executed (one for the Get, one for the Query), but both variables contain the same object reference.

Now, if you enable the 2nd level cache, query caching, and specify caching for the query:

var fooQueryById = session.Query<Foo>().Cacheable()
                          .Single(f => f.Id == fooId);
var fooQueryByIdAgain = session.Query<Foo>().Cacheable()
                               .Single(f => f.Id == fooId);

Only one query will be executed.

Answer 2

No, as I understand they don't. They use only second level cache. Firs level cache is only for Get and Load.