NHibernate with string primary key and relationships

return session.Get<T>(id);

<class name="Merchant" table="T__MERCHANT">
        <id name="MerchantId" column="MERCHANT_ID" type="string">
            <generator class="assigned" />
        </id>

        <property name="MerchantStatusId" column="MERCHANT_STATUS_ID" type="Char" not-null="true" length="1" />
        <property name="MerchantStatusName" column="MERCHANT_STATUS_NAME" type="string" length="50" />
        <property name="MerchantName" column="NAME" type="string" not-null="true" length="50" />
 </class>
</hibernate-mapping>

public Merchant GetMerchantById(string id)
{
     return session.Get<Merchant>(id);
}

<joined-subclass name="JohnHarmanLtd.Web.FineArtCompany.Models.Book, App_Code.tqeub3fb, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null">

Imports NHibernate.UserTypes
Imports NHibernate.Type
Imports NHibernate.SqlTypes

Public Class CaseInsensitiveStringType
    Inherits AbstractStringType

    ' Methods
    Public Sub New()
        MyBase.New(New StringSqlType)
    End Sub

    Public Sub New(ByVal sqlType As StringSqlType)
        MyBase.New(sqlType)
    End Sub


    ' Properties
    Public Overrides ReadOnly Property Name As String
        Get
            Return "InsensitiveString"
        End Get
    End Property

    Public Overrides Function IsEqual(ByVal x As Object, ByVal y As Object) As Boolean
        Return MyBase.IsEqual(x, y) OrElse (x IsNot Nothing AndAlso y IsNot Nothing AndAlso String.Equals(x, y, StringComparison.InvariantCultureIgnoreCase))
    End Function

    Public Overrides Function GetHashCode(ByVal x As Object, ByVal entityMode As NHibernate.EntityMode, ByVal factory As NHibernate.Engine.ISessionFactoryImplementor) As Integer
        Return MyBase.GetHashCode(x.ToString().Trim().ToUpperInvariant(), entityMode, factory)
    End Function
End Class

Id(Function(x) x.Id).GeneratedBy.Assigned().CustomType(Of CaseInsensitiveStringType)()

Example.create(parent).ignoreCase()