Using Sqlite to test database interaction with NHibernate

In a previous post, Stubbing Out NHibernate's ISession, I talked about creating a mock class in order to stub out QueryOver interaction in your classes. In this post I'd like to talk about another approach to take: using an in-memory Sqlite database to simulate real data interaction. The upside to using an in-memory Sqlite database, is that you can quickly test to make sure if your query will actually work as you expect it to work. There are a couple of downsides, however. One is that you're using Sqlite as opposed to whatever production grade database you will be using in deployment. The second, is that set-ups for your tests can get pretty complex, as you may potentially need to persist a lot of entities.

The first thing you'll need to do, is to download Sqlite and the appropriate .NET wrapper. These can be found here and here respectively. Next you'll need to create some sort NHibernate session manager. This class should be able to create an in-memory Sqlite database, create the schema, and open an ISession. Here's  what mine looks like

public class NHibernateSqliteSessionFactory
{
 private static readonly NHibernateSqliteSessionFactory _instance = new NHibernateSqliteSessionFactory();
 private static Configuration _configuration;
 private readonly ISessionFactory _sessionFactory;

 private NHibernateSqliteSessionFactory()
 {
  var model = AutoMap.AssemblyOf<Entity>(new GasOverBitumenConfiguration())
   .UseOverridesFromAssemblyOf<NHibernateSessionFactory>()
   .Conventions.Add(
    DefaultLazy.Always(),
    DynamicUpdate.AlwaysTrue(),
    DynamicInsert.AlwaysTrue())
   .Conventions.AddFromAssemblyOf<Entity>();

  FluentConfiguration fluentConfig = Fluently.Configure()
   .Database(
    new SQLiteConfiguration()
     .InMemory()
     .UseReflectionOptimizer()
   )
   .ProxyFactoryFactory("NHibernate.ByteCode.Castle.ProxyFactoryFactory, NHibernate.ByteCode.Castle")
   .Mappings(m =>
        {
         m.AutoMappings.Add(model);
         m.FluentMappings.AddFromAssemblyOf<Entity>();
        })
   .ExposeConfiguration(c => _configuration = c);

  _sessionFactory = fluentConfig.BuildSessionFactory();
 }

 public static NHibernateSqliteSessionFactory Instance
 {
  get { return _instance; }
 }

 public ISession OpenSession()
 {
  var session = _sessionFactory.OpenSession();
  new SchemaExport(_configuration).Execute(false, true, false, session.Connection, new StringWriter());
  session.BeginTransaction();
  return session;
 }
}

Note that we are using FluentNhibernate to create the configuration. This can be just as easily accomplished with either traditional or loquacious configuration. Furthermore the OpenSession method creates a session and sets up the database schema. When the session is closed, the in-memory database is gone.

It might be a good idea to also persist several entities in your database, such that your unit tests are not required to have large set up methods. Your test can then simply open the session, do what is being tested and verify that the result is correct. In your clean up step, it's a good idea to dispose the session.

There you have it. An easy way to set up an in-memory Sqlite database for NHibernate.