Database per tenant with Fluent NHibernate & StructureMap

Question

I'm currently using StructureMap to inject an NHibernateRegistry instance into my DAL, which configures NHibernate for a single connection string and bootstraps a Singleton FluentConfiguration for my single-user app.

How should I modify my Fluent NHibernate configuration to use a different database based on a {tenant} routing parameter in my routing URL?

Routing example:

{tenant}/{controller}/{action}/{id}

...where requests for branch1/Home/Index and branch2/Home/Index use the same application code, but different databases to retrieve the data displayed.

I solved this problem in the past for StructureMap and LINQ by injecting a per-request TenantContext object, which retrieved the routing parameter from the HttpContext it accepted as a constructor parameter and specified a different LINQ data context.

However, I suspect NHibernate has a better of handling this than I could cook up.

Partial NHibernateRegistry class

public class NHibernateRegistry : Registry
{
    // ... private vars here

    public NHibernateRegistry()
    {
        var cfg = Fluently.Configure()
            .Database(MsSqlConfiguration
                .MsSql2008.ConnectionString(c => 
                    c.FromConnectionStringWithKey("TenantConnectionStringKey")))
                    // where to inject this key?
            .ExposeConfiguration(BuildSchema)
            .Mappings(x => 
                x.FluentMappings.AddFromAssembly(typeof(UserMap).Assembly)

        For<FluentConfiguration>().Singleton().Use(cfg);

        var sessionFactory = cfg.BuildSessionFactory();

        For<ISessionFactory>().Singleton()
            .Use(sessionFactory);
        For<ISession>().HybridHttpOrThreadLocalScoped()
            .Use(x => x.GetInstance<ISessionFactory>().OpenSession());
        For<IUnitOfWork>().HybridHttpOrThreadLocalScoped()
            .Use<UnitOfWork>();
        For<IDatabaseBuilder>().Use<DatabaseBuilder>();

    }
}

StructureMap configuration:

public static class Bootstrapper
{
    public static void ConfigureStructureMap()
    {
        ObjectFactory.Initialize(Init);
    }

    private static void Init(IInitializationExpression x)
    {
        x.AddRegistry(new NHibernateRegistry()); // from Data project
    }
}

I'm new to NHibernate, so I am unsure of scoping my sessions and configurations. Does NHibernate have a built-in way to handle this?

Answer 1

This worked for me in an a module

return Fluently.Configure()
            .Database(MsSqlConfiguration.MsSql2008.ConnectionString(x => x.FromConnectionStringWithKey("IMB"))
            .Cache(c => c.UseQueryCache().QueryCacheFactory<StandardQueryCacheFactory>()
                         .RegionPrefix("IMB")
                         .ProviderClass<HashtableCacheProvider>()
                         .UseMinimalPuts()).UseReflectionOptimizer())
            .Mappings(m => m.FluentMappings.AddFromAssembly(Assembly.Load("IMB.Data")))
           .Mappings(m => m.FluentMappings.AddFromAssembly(Assembly.Load("IMB.Security")))

           .ExposeConfiguration(
            c => c.SetProperty("current_session_context_class", "web"))
            .ExposeConfiguration(cfg => _configuration = cfg)
            .BuildSessionFactory();

Answer 2

The problem is that you really want your ISessionFactory object to be a singleton. This means its best not to specify the connection string when creating the ISessionFactory. Have your tried creating the ISessionFactory without specifying a connection string and then passing a manually created connection to ISessionFactory.OpenSession?

For example:

public ISession CreateSession()
{
    string tennantId = GetTennantId();
    string connStr = ConnectionStringFromTennant(tennantId);
    SqlConnection conn = new SqlConnection(connStr);
    conn.Open();
    session = sessionFactory.OpenSession(conn);
}

And then tell StructureMap to call this method.

The downside is that you can't now from build the database schema when creating the ISessionFactory, but maybe creating database schemas in web applications isn't that great an idea anyway?