NHibernate
 | This article contains promotional content. (March 2012) |
| Stable release | 3.2.0
/ July 30, 2011 |
|---|---|
| Repository | |
| Written in | C# |
| Operating system | Cross-platform |
| Platform | .NET 1.1 or 2.0 or 3.5 or 4.0 and Mono |
| Type | Object-relational mapping |
| License | GNU Lesser General Public License |
| Website | nhforge |
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.
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]) mk,
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 was released in April, 2011.
What is new in NHibernate 3.2
Some of the new Features are [4]
- Mapping by code: fluent configuration, .hbm.xml files are no longer 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 add an object to the database and shows how to to retrieve, modify and update an object in the database using NHibernate.
//Add a Customer to the datastore
//'sessionFactory' is a thread-safe object built once per application lifetime (can take seconds to build)
//based on configuration files which control how database tables are mapped to C# objects
//(e.g. which property maps to which column in a database table)
//
//'session' is not thread-safe and fast to obtain and can be thought of as a connection to the database
using (var session = sessionFactory.OpenSession())
{
//transaction represents a db transaction
using (ITransaction transaction = session.BeginTransaction())
{
//The line below adds the customer to NHibernate's list of objects to insert to the database
//but it doesn't execute SQL insert command at this stage*.
//*if the Id field is generated by the database (e.g. an auto-incremented number)
//then NHibernate will execute SQL INSERT when .Save is called
session.Save(new Customer { Id = Guid.NewGuid(), FirstName = "Bill", Age = 50 });
//The call below will execute the SQL INSERT and commit the transaction
transaction.Commit();
}
}
//Retrieve the Customer from the database, modify the record and update the database
using (var session = sessionFactory.OpenSession())
using (ITransaction transaction = session.BeginTransaction())
{
//session's Query returns IQueryable<Customer>.
//Only when .FirstOrDefault is called NHibernate will execute the SQL query
Customer customer = session.Query<Customer>().Where(c => c.Token == token ).FirstOrDefault();
//Now the customer is 'part of' the 'session' object and NHibernate keeps track of changes
//made to it
if( customer != null )
{
//Changing a property of an object does NOT cause SQL to be executed
customer.TokenVerified = true;
//Committing the transaction results is an SQL UPDATE statement
//NHibernate kept track of the fact that 'customer' has been changed since loading
transaction.Commit();
}
}
It must be noted here that NHibernate's configuration may affect when NHibernate executes SQL statements.
See also
References
Bibliography
- Dentler, Jason (October 4, 2010). NHibernate 3.0 Cookbook (1st ed.). Packt Publishing. ISBN 1849513043.
{{cite book}}: Check|isbn=value: checksum (help) - Cure, Aaron (May 5, 2010). NHibernate 2 Beginner's Guide (1st ed.). Packt Publishing. ISBN 1847198902.
- Kuaté, Pierre Henri; Harris, Tobin; Bauer, Christian; King, Gavin (February 2009). NHibernate in Action. Manning Publications. ISBN 1932394923.
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