I've already developed some projects with NHibernate and I can say that NHibernate is a real time saver. But I must admit that it takes some time to get used to NHibernate. As an ORM NHibernate has fantastic features but if you want to develop successfull projects with NHibernate you must know that NHibernate is only one part (ORM) of a successfull layered architecture. In the attached solution I tried to give you the basic idea of a layered architecture and how NHibernate can be used within such an architecture

Attached solution includes the following projects

• Core: Our domain objects (entities) reside in this layer. Also DAO (Data Access Objects) interfaces are defined in this layer.
  
• DAL (Data Access Layer): Default implementation of DAO interfaces reside in this layer.
  
• BLL (Business Logic Layer): Business logic code resides in this layer.
  
• Common: Some utility calsses reside in this project
  
• Tests.Disconnected: Includes unit tests for domain objects and business logic. Notice that unit tests in this project do not require domain objects to be persisted (NHibernate behaviour will not be tested), so the need for a database connection is eliminated which in turn makes our unit tests fast. Notice how we replaced our default DAL with mocked one.
  
• Tests.Connected: This project includes unit tests too, but this time we want to test how our domain objects and bussiness logic perform NHibernate. NHibernate provides very cool features like native sql, lazy loading and cascading and we will likely want to test how our domain objects behave when armored with these cool features of NHibernate. It is also very likely that we will have some mapping errors (typos likely) in our Core, these tests will help us catch these errors. Performance bottlenecks possibly caused by our NHibernate mappings (for example we may discover that we need to make a child collection to be lazy loaded) can also be identified with help of these tests.

In the sample solution you can also find a simple usage of Castle Windsor Inversion of Control (IoC) container. We use IoC to be able to load different implementations of our DAL (DAO implementations). 

Another very important point you need to understand really well is session management of NHibernate when used in web applications. Thanks to Burrow contribution project this task is made very simple, you do not even need to write single line of NHibernate session management code. You only need to inherit your DAO implementation classes from GenericDao<T> class and you are ready to go. 

Additional Notes

• Database script is included in Tests.Connected project under DBScript folder. 
• Sample project uses NHibernate  2.0 Aplha1 and NHibernate.Burrow is also Alpha1.
• ASP .NET MVC Preview 3 to run Sales.MVC sample
• TestDriven .NET to run NUnt tests
  

Suggested Readings

• NHibernate Reference Documentation
• NHibernate Quick Start Guide
• NHibernate In Action  by Pierre Henri Kuaté, Tobin Harris, Christian Bauer, and Gavin King
  
• NHibernate Best Practices with ASP .NET by Billy McCafferty

Downloads

• SalesSample.rar (5,61 mb)

Update History

• 09 June 2008
  • Castle files under Libs folder updated to Castle RC3
  • SQLite references removed
  • TestFixtureTearDown override of CustomTestBase class in Sales.Tests.Connected assembly commented out