Integrating Fluent NHibernate and the Windsor NHibernate Facility

Our current project uses NHibernate as its ORM. Until recently we've been using the default hbm mapping files, but we've been suffering for some time from Fluent NHibernate envy. So now we've decided to take the plunge and migrate our project to code based mapping. My esteemed colleague Keith Bloom has been doing most of the work for this, and this post is simply me taking a free ride on all his hard work. Thanks Keith :)

I'm not going to describe Fluent NHibernate here. You can check out the project page if you want to see what it's all about. Suffice to say that it's a really nice API to describe object-relational mapping. Once you've defined your mappings, it's a simple case of applying them to the NHibernate configuration with a handy extension method:

var cfg = new Configuration()
	.Configure()
	.LoadMappingAssembly(Assembly.LoadFrom("Name of assembly that contains your maps."));

However we're using Windsor's very convenient NHibernate integration facility in our project. It does all the configuration and session management for us, so we don't have to worry about it. The problem is, that because it handles it for us, there's not an immediately obvious place to access the configuration to apply the Fluent NHibernate mappings.

It turns out that the simplest way of doing this is to write your own implementation of IConfigurationBuilder. This is the NHibernate facility class that actually creates the NHibernate configuration:

public class FluentNHibernateConfigurationBuilder : IConfigurationBuilder
{
	public Configuration GetConfiguration(IConfiguration facilityConfiguration)
	{
	    var defaultConfigurationBuilder = new DefaultConfigurationBuilder();
	    var configuration = defaultConfigurationBuilder.GetConfiguration(facilityConfiguration);
             configuration.AddMappingsFromAssembly(Assembly.LoadFrom("Name of assembly that contains your maps."));
	    return configuration;
	}
}

Note that we're simply deferring the creation of the NHibernate configuration to the DefaultConfigurationBuilder and then adding the call to to AddMappingsFromAssembly before passing it on. All we have to do now is configure the facility to use our new configuration builder:

<facility id="nhibernate"
          isWeb="false"
          type="Castle.Facilities.NHibernateIntegration.NHibernateFacility, Castle.Facilities.NHibernateIntegration"
          configurationBuilder="Keith.WindsorNHibernate.Services.FluentNHibernateConfigurationBuilder, Keith.WindsorNHibernate">
  <factory id="nhibernate.factory">
    <settings>
      <item key="show_sql">true</item>
      <item key="connection.provider">NHibernate.Connection.DriverConnectionProvider</item>
      <item key="connection.driver_class">NHibernate.Driver.SqlClientDriver</item>
      <item key="dialect">NHibernate.Dialect.MsSql2005Dialect</item>
      <item key="connection.connection_string">Data Source=.\SQLEXPRESS;Initial Catalog=Northwind;Integrated Security=True</item>
    </settings>
  </factory>
</facility>

Keith has kindly allowed me to post his test solution which you can download below. You'll need sqlexpress with a copy of Northwind to run it.

http://static.mikehadlow.com/Keith.WindsorNHibernate.zip