As we saw in the earlier article Code First Entity Framework, Microsoft have given us an ORM solution which works out of the box. As an alternative to using theirs, an older ORM framework called nHibernate has been around for a few years. This is slightly more mature than EF, and is used in lots of places.

nHibernate comes in two flavours = XML configuration for mappings, and Fluent API. Let's start with the older version, which uses XML to map columns and classes.

Let's create a table in the database:

CREATE TABLE [dbo].[tbl_contact](
	[contact_id] [bigint] IDENTITY(1,1) NOT NULL,
	[first_name] [varchar](255) NULL,
	[last_name] [varchar](255) NULL,
	[email] [varchar](255) NULL,
	[telephone] [varchar](50) NULL,
    CONSTRAINT [PK_tbl_contact] PRIMARY KEY CLUSTERED ( [contact_id] ASC )
) 

As you can see, this creates a table with a few customer related fields, with an Id primary key which is also an identity column generated by the database itself.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace TestnHibernate.Entity
{
    public class Contact
    {
        public virtual int ContactId { get; set; }

        public virtual string FirstName { get; set; }

        public virtual string LastName { get; set; }

        public virtual string Email { get; set; }

        public virtual string Telephone { get; set; }

        public  Contact()
        {
        }
    }
}

So, if we want to use nHibernate to do our ORM, we need to ge the dlls from here. Unzip the download and add references to the binaries contained in it to your Contact project. For older versions of nHibernate, the core and fluent versions were in different dlls, but more modern versions (3.2 upwards) package all into a single nHibernate dll.

XML Configuration - Add the following to the web.config of your app

  <configSections>
    <section name="hibernate-configuration" type="NHibernate.Cfg.ConfigurationSectionHandler, NHibernate" />
  </configSections>

  <hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
    <session-factory>
      <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
      <property name="dialect">NHibernate.Dialect.MsSql2005Dialect</property>
      <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
      <property name="connection.connection_string">Data Source=localhost;Initial Catalog=test;Integrated Security=True</property>
      <property name="proxyfactory.factory_class">NHibernate.ByteCode.Castle.ProxyFactoryFactory, NHibernate.ByteCode.Castle</property>
    </session-factory>
  </hibernate-configuration>

Now, in the same place as you stored your Contact.cs file, create a small XML document called Contact.hbm.xml

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="testnHibernate" assembly="testnHibernate">
  <class name="Contact" table="tbl_contact">
    <id       name="ContactId"  column="contact_id" type="int"><generator class="identity"></generator></id>
    <property name="FirstName"  column="first_name" type="String"/>
    <property name="LastName"   column="last_name"  type="String"/>
    <property name="Email"      column="email"      type="String"/>
    <property name="Telephone"  column="telephone"  type="String"/>
  </class>
</hibernate-mapping>

        ...
      
        // setup nhibernate configuration
        NHibernate.Cfg.Configuration config = new NHibernate.Cfg.Configuration();
        config.AddAssembly(typeof(Contact).Assembly);
        NHibernate.ISessionFactory factory = config.BuildSessionFactory();
        NHibernate.ISession session = factory.OpenSession();
        NHibernate.ITransaction transaction = session.BeginTransaction();

        // create a contact from the form data (or if MVC, bound ViewModel properties or FormCollection)
        Contact contact = new Contact();
        contact.FirstName = txtFirstName.Text;
        contact.LastName = txtLastName.Text;
        contact.Email = txtEmail.Text;
        contact.Telephone = txtTelephone.Text;

        // tell NHibernate that this object should be saved and commit
        session.Save(contact);
        transaction.Commit();
        session.Close();

        ...

        // fetch a single contact from the database by id
        Contact singleContact = session.Get<Contact>(1);

        // fetch all contacts from the database 
        List<Contact> allContacts = (List<Contact>)session.CreateCriteria(typeof(Contact)).List<Contact>();

    public class ContactFluentMap : ClassMap<Contact>
    {
        public ContactFluentMap()
        {
            Table("tbl_contact");
            Id(x => x.ContactId).Column("Contact_Id");
            Map(x => x.FirstName).Column("First_Name");
            Map(x => x.LastName).Column("Last_Name");
            Map(x => x.Email);
            Map(x => x.Telephone);
        }
    }

    private static ISessionFactory CreateSessionFactory()
    {
        return Fluently.Configure()
            .Database(MsSqlConfiguration.MsSql2008.ConnectionString(c => c.FromConnectionStringWithKey("connectionStringKey")))
            .Mappings(m => m.FluentMappings.Add(typeof(ContactFluentMap)))
            .BuildSessionFactory();
    }

        var sessionFactory = CreateSessionFactory();
        using (var session = sessionFactory.OpenSession())
        {
            var transaction = session.BeginTransaction();
            // create contact
            Contact contact = new Contact();
            contact.FirstName = txtFirstName.Text;
            contact.LastName = txtLastName.Text;
            contact.Email = txtEmail.Text;
            contact.Telephone = txtTelephone.Text;
            session.Save(contact);
            transaction.Commit();
        }