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Fluent NHibernate

Posted by Hartmut Wilms on Aug 13, 2008 11:02 PM

Community: .NET
Topics: Data Access ,; Domain Specific Languages
Tags: ORM ,; nHibernate

Fluent NHibernate is an API for creating NHibernate mappings programmatically instead of XML configuration files. Its goal is to reduce the difficulties faced when incorporating NHibernate in a project by providing improved readability, testing capabilities, and compile time safety.

James Gregory, project owner, introduces Fluent NHibernate and raises his concerns about NHibernate’s XML configuration files:

[…] I think we all also have a bit of a dislike for the amount of XML you need to write to get your classes mapped; not only that, but also how the mappings are distinctly separate from the rest of your application. They’re often neglected and untested. One of the core tenets of the project is that we need a more succinct, readable, and testable way of writing your mappings.

In addition, Fluent NHibernate provides a fluent interface. Piers Cawley provides a good summary and explains that “client side complexity […] is reduced by moving object construction behind a thoughtful, humane interface”.

Fluent NHibernate reduces the complexity further by adhering to the convention over configuration principle, which means that the most common setup for any part of a mapping is chosen by default.

Besides compile time checking Fluent NHibernate adds to the robustness of your mappings by providing an API for testing. “We also want to help you verify that your mappings are set up properly, not just syntactically valid”, says James Gregory.

Last but not least Fluent NHibernate features a framework, which helps to setup a reference architecture and plays well with your IoC container of choice:

Our framework is a layer that sits on-top of the API to provide an even better experience. We’re looking to integrate with your favorite container, which will reduce the code you need to write to integrate NHibernate into your system. Then we’re going to tackle extensible conventions, which will allow you to specify your own implied conventions for your application. For example, if you’re always going to call your identifier “ID”, then why should you have to specify it every time? You shouldn’t!

Bobby Johnson gives a detailed step-by-step example of using Fluent NHibernate in his article “Skinning the Cat with Fluent NHibernate”.