if (sql.CommandType == CommandType.Text)
{
          insertSelectSQL = Dialect.AddIdentitySelectToInsert(text, GetKeyColumns(0)[0], GetTableName(0));
}

if (sql.CommandType == CommandType.Text)
{
          insertSelectSQL = AddIdentitySelectToInsert(sql.Text);         
}

    protected virtual SqlString AddIdentitySelectToInsert(SqlString text)
    {
      return Dialect.AddIdentitySelectToInsert(text, GetKeyColumns(0)[0], GetTableName(0));
    }

Imports NHibernate
Imports NHibernate.Persister.Entity
Imports NHibernate.Mapping
Imports NHibernate.Cache
Imports NHibernate.Engine


Namespace ORM.Extensions

   Public Class CompositeIdentityTablePersister
      Inherits NHibernate.Persister.Entity.SingleTableEntityPersister

      Public Sub New(ByVal model As PersistentClass, ByVal cache As ICacheConcurrencyStrategy, _
       ByVal factory As ISessionFactoryImplementor, ByVal mapping As IMapping)
         MyBase.New(model, cache, factory, mapping)
      End Sub

      Public Overrides ReadOnly Property IdentifierGenerator() As NHibernate.Id.IIdentifierGenerator
         Get
            Return New NHibernate.Id.IdentityGenerator
         End Get
      End Property

      Public Overrides ReadOnly Property IsIdentifierAssignedByInsert() As Boolean
         Get
            Return True
         End Get
      End Property

      ''' <remarks>
      ''' We override this so we can return a null identifier if the ID is zero, which allows IsUnsaved in the persister to
      ''' spot this record needs saving
      ''' </remarks>
      Public Overrides Function GetIdentifier(ByVal obj As Object) As Object
         Dim key As DBKey = MyBase.GetIdentifier(obj)
         If key Is Nothing OrElse key.ID = 0 Then Return Nothing
         Return key
      End Function

      ''' <remarks>
      ''' Had to modify the base class AbstractEntityPersister to make this overridable
      ''' </remarks>
      Protected Overrides Function GetGeneratedIdentity(ByVal obj As Object, ByVal session As NHibernate.Engine.ISessionImplementor, ByVal rs As System.Data.IDataReader) As Object
         Dim id As DBKey = New DBKey
         Try
            If Not rs.Read() Then Throw New HibernateException("The database returned no natively generated identity value")
            id.ID = rs(0)
            id.Prefix = rs(1)
         Finally
            rs.Close()
         End Try
         Return id
      End Function

      ''' <remarks>
      ''' Had to extract this method from the Protected Insert method of the AbstractEntityPersister
      ''' </remarks>
      Protected Overrides Function AddIdentitySelectToInsert(ByVal text As NHibernate.SqlCommand.SqlString) As NHibernate.SqlCommand.SqlString
         ' Need to get the field names for the Prefix and ID columns
         Dim IDField As String = If(IdentifierColumnNames(0).EndsWith("ID"), IdentifierColumnNames(0), IdentifierColumnNames(1))
         Dim PrefixField As String = If(IdentifierColumnNames(0).EndsWith("ID"), IdentifierColumnNames(1), IdentifierColumnNames(0))
         ' Also need to identify which parameter contains the passed in prefix
         ' We'll assume that the first three parts are "INSERT INTO ", tablename and a comma, and that each field is
         ' separated by a comma
         Dim ValPartIndex As Integer = 0, PrefixIndex As Integer = -1
         For partindex As Integer = 4 To text.Parts.Count - 1 Step 2
            If text.Parts(partindex) = ") VALUES (" Then
               ValPartIndex = partindex
               Exit For
            End If
         Next
         For partindex As Integer = 3 To ValPartIndex Step 2
            If text.Parts(partindex) = "Prefix" Then
               PrefixIndex = (partindex - 3) / 2
               Exit For
            End If
         Next
         Return text.Append(String.Format("; SELECT SCOPE_IDENTITY() AS {0}, @p{2} AS {1}", IDField, PrefixField, PrefixIndex))
      End Function

   End Class

End Namespace

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="Domain" assembly="Saturn.DAO">
   <class name="Saturn.DAO.Domain.Client, Saturn.DAO" table="Clients" persister="Saturn.DAO.ORM.Extensions.CompositeIdentityTablePersister, Saturn.DAO">
<!-- Identity -->
    <composite-id name="ID" class="Saturn.DAO.Types.DBKey">
      <key-property name="Prefix"/>
      <key-property name="ID"/>
    </composite-id>