Creating a custom user type in Nhibernate

NHibernate has the concept of a User Type. It allows you to specify how a custom type should be mapped between your object model and the database.

An example of an out-of-the-box User Type is the YesNo type. This type allows you to map (“Y”/”N”) values in your database to boolean values in your application. To use this in your application you only need to specify a type in your mapping file:

<property name="IsActive" type="YesNo"/>

For a project I’m working on, I had a similar requirement, but because the application was in Dutch I had to use “J”/”N” instead of “Y”/”N”.

So let’s build our own User Type to achieve this. The nice thing is that I don’t have to start from scratch but can extend one of the existing User Types:

	using System;
	using System.Collections.Generic;
	using System.Linq;
	using System.Text;
	using NHibernate.Type;
	using NHibernate.SqlTypes;
	namespace NHibernate
	{
	/// <summary>
	/// This is a custom type that can be used to map a boolean field to a char field with the values 'J' and 'N' in the database.
	/// </summary>
	public class JaNeeType : CharBooleanType
	{
	/// <summary>
	/// Initializes a new instance of the <see cref="JaNeeType"/> class.
	/// </summary>
	public JaNeeType()
	: base(new AnsiStringFixedLengthSqlType(1))
	{
	}
	/// <summary>
	/// True value= 'N'
	/// </summary>
	/// <value></value>
	protected sealed override string FalseString
	{
	get
	{
	return "N";
	}
	}
	/// <summary>
	/// Gets the name.
	/// </summary>
	/// <value>The name.</value>
	public override string Name
	{
	get
	{
	return "JaNee";
	}
	}
	/// <summary>
	/// True value= 'J'
	/// </summary>
	/// <value></value>
	protected sealed override string TrueString
	{
	get
	{
	return "J";
	}
	}
	}
	}

view raw JaNeeType.cs hosted with ❤ by GitHub

To use this type in our application, we have to change the mapping to:

<property name="IsActive" type="NHibernate.JaNeeType,Sample.NHibernate"/>