Look on my works, ye Mighty, and despair!

If you are using NHibernate for data access, and have to access more than one database, then you need a way of managing multiple Session Factories.

Ideally, your repositories (or whatever) would only take a dependency on an ISession, without needing to know where it came from (DIP). But if you’re getting these repositories out of a container, then you have a problem. How do you provide a different ISession to different instances?

One solution is to use named instances. The following example is for StructureMap, other containers are available. :)

public class NHibernateRegistry : Registry
{
    public NHibernateRegistry()
    {
        const string connectionString1 = "theNameOfAConnectionStringInAppConfig";
        const string connectionString2 = "theNameOfADifferentConnectionStringInAppConfig";

        For<ISessionFactory>()
            .Singleton()
            .Use(SessionFactory.BuildFor(connectionString1))
            .Named(connectionString1);

        For<ISessionFactory>()
            .Singleton()
            .Use(SessionFactory.BuildFor(connectionString2))
            .Named(connectionString2);

        For<ISession>()
            .Use(c => c.GetInstance<ISessionFactory>(connectionString1).OpenSession())
            .Named(connectionString1);

        For<ISession>()
            .Use(c => c.GetInstance<ISessionFactory>(connectionString2).OpenSession())
            .Named(connectionString2);

        For<ISomethingRepository>()
            .Ctor<ISession>("session").Use(c => c.GetInstance<ISession>(connectionString1));

        For<ISomethingElseRepository>()
            .Ctor<ISession>("session").Use(c => c.GetInstance<ISession>(connectionString2));
    }
}

Or maybe, in the future, just:

For<ISomethingElseRepository>()
    .Ctor<ISession>("session").Named(connectionString2);