NHibernate

This article is about the .NET and Mono library. For other uses, see Hibernate.

NHibernate

Stable release	3.2.0 / July 30, 2011; 3 months ago (2011-07-30)
Written in	C#
Operating system	Cross-platform
Platform	.NET 1.1 or 2.0 or 4.0 and Mono
Type	Object-relational mapping
License	GNU Lesser General Public License
Website	nhforge.org

Free software portal

NHibernate is an object-relational mapping (ORM) solution for the Microsoft .NET platform: it provides a framework for mapping an object-oriented domain model to a traditional relational database. Its purpose is to relieve the developer from a significant portion of relational data persistence-related programming tasks. NHibernate is free as open source software that is distributed under the GNU Lesser General Public License. NHibernate is a port of the popular Java O/R mapper Hibernate to .NET. NHibernate provides transparent persistence for Plain Old CLR Objects (POCOs). The only strict requirement for a persistent class is a no-argument constructor, which does not have to be public. (Proper behavior in some applications also requires special attention to the Equals() and GetHashCode() methods.^[1])

Feature summary

NHibernate's primary feature is mapping from .NET classes to database tables (and from CLR data types to SQL data types). NHibernate also provides data query and retrieval facilities. NHibernate generates the SQL commands and relieves the developer from manual data set handling and object conversion, keeping the application portable to most SQL databases, with database portability delivered at very little performance overhead.

NHibernate provides transparent persistence for Plain Old CLR Objects (POCOs). The only strict requirement for a persistent class is a no-argument constructor, which does not have to be public. (Proper behavior in some applications also requires special attention to the Equals() and GetHashCode() methods.[1])

History

NHibernate was started by Tom Barrett, and later picked up by Mike Doerfler and Peter Smulovics. Now Fabio Maulo is the project leader. At the end of 2005, JBoss, Inc. (now part of Red Hat) hired Sergey Koshcheyev, the then lead developer of NHibernate, to work full-time on its future versions.^[2] At the end of 2006 JBoss stopped the support to this project; it is now entirely developed and led by the community.

Version 1.0 mirrored the feature set of Hibernate 2.1, as well as a number of features from Hibernate 3.

NHibernate 1.2.1, released in November 2007, introduced many more features from Hibernate 3 and support for .NET 2.0, stored procedures, generics, and nullable types.

NHibernate 2.0 was released August 23, 2008. It is comparable to Hibernate 3.2 in terms of features. With the version 2.0 release, NHibernate dropped support for .NET 1.1.^[3]

NHibernate 2.1 was released July 17, 2009.

NHibernate 3.0 was released on December 04, 2010 and is the first version to use .NET 3.5. Introduces integrated LINQ support and also strongly typed criteria-like API called QueryOver, new AST-based parser for NHibernate's HQL (Hibernate Query Language) engine, support for lazy loading columns.

NHibernate 3.2 has been released recently.

What is new in NHibernate 3.2

Some of the new Features are ^[4]

• Mapping by code: fluent configuration, no more .hbm.xml files required;
• Subselect: ability to map SQL views as entities;
• HQL paging: TAKE and SKIP on HQL;
• Integrated bytecode provider: one less DLL to deploy.

Contributions

As open source software, NHibernate has received many contributions from its users. Most of them are directly integrated as internal features. Others are provided by the users as utilities and documentation.

Implementation of LINQ has allowed Language Integrated Query use with NHibernate.^[5]

Sample

Here a code snippet to save and retrieve an object using NHibernate:

////Save a Customer
using (var session = sessionFactory.OpenSession()) 
{
    using (ITransaction transaction = session.BeginTransaction()) 
    {
        session.Save(new Customer { Id = Guid.NewGuid(), FirstName = "Bill", Age = 50 });
        transaction.Commit();
    }
}
 
////Retrieve the Customer
using (var session = sessionFactory.OpenSession()) 
{
    var customer = session.Query<Customer>().Single(c => c.Id == id);
}

See also

• List of object-relational mapping software

References

1. ^ hibernate.org - Equals and HashCode
2. ^ [Hibernate] NHibernate joins Hibernate at JBoss Inc
3. ^ nhforge.org - from NH1.2.1GA to NH2.0.0
4. ^ weblogs.asp.net - New features in nHibernate 3.2
5. ^ Implementing Linq for NHibernate: A How To Guide - Part 1

Bibliography

• Dentler, Jason (October 4, 2010). NHibernate 3.0 Cookbook (1st ed.). Packt Publishing. ISBN 1849513043. https://www.packtpub.com/nhibernate-3-0-cookbook/book. 
• Cure, Aaron (May 5, 2010). NHibernate 2 Beginner's Guide (1st ed.). Packt Publishing. ISBN 1847198902. https://www.packtpub.com/nhibernate-2-x-beginners-guide/book. 
• Kuaté, Pierre Henri; Harris, Tobin; Bauer, Christian; King, Gavin (February 2009). NHibernate in Action. Manning Publications. ISBN 1932394923. 

External links

• NHibernate Homepage
• NHibernate Sourceforge Summary
• NHibernate overview by Justin Gehtland Part 2
• NuGet NHibernate package