public class Program
    {
        private static Configuration cfg;
        private static ISessionFactory sf;
        private static ISessionFactory sessionFactory;

        private static void Main()
        {
            #region Init
            cfg = new Configuration();
            cfg.SetProperty("connection.driver_class", "NHibernate.Driver.SqlClientDriver");
            cfg.SetProperty("hibernate.search.default.directory_provider", "NHibernate.Search.Storage.FSDirectoryProvider, NHibernate.Search");
            cfg.SetProperty("hibernate.search.default.indexBase", @"~\Index");
            cfg.SetProperty("hibernate.search.analyzer", "Lucene.Net.Analysis.Standard.StandardAnalyzer, Lucene.Net");
            cfg.SetProperty("cache.use_query_cache", "false");
            cfg.SetProperty("connection.provider", "NHibernate.Connection.DriverConnectionProvider");
            cfg.SetProperty("dialect", "NHibernate.Dialect.MsSql2005Dialect");
            cfg.SetProperty("connection.connection_string", @"server=PC-VIL8-NEW\LOCALTEST;initial catalog=OrbitorHR;user id=sa;password=Zip8920n;Connection Timeout=40;");
            cfg.SetProperty("show_sql", "true");
            cfg.Configure();
            sessionFactory = cfg.BuildSessionFactory();
            SearchFactory.Initialize(cfg, sessionFactory);
            ISession session = sessionFactory.OpenSession(new SearchInterceptor());
            IFullTextSession fullTextSession = Search.CreateFullTextSession(session);
            #endregion

            string query = "admin";
            Analyzer analyzer = new SimpleAnalyzer();
            MultiFieldQueryParser parser = new MultiFieldQueryParser(
                                           new string[] { "UserName", "LoweredUserName" },
                                           analyzer);
            Query queryObj = null;
            try
            {
                queryObj = parser.Parse(query);
            }
            catch (ParseException) { }
            IFullTextSession session2 = fullTextSession;
            IQuery nhQuery = session2.CreateFullTextQuery(queryObj, new Type[] { typeof(User) });
            IList<User> users = nhQuery.List<User>();
            Console.ReadKey(true);
        }
}

using System;
using System.Collections.Generic;
using System.Text;
using NHibernate.Search;
using NHibernate.Search.Attributes;
using NHibernate.Search.Bridge.Builtin;
using Lucene.Net.Analysis.Standard;

namespace NHibernateSearch_Demo.Model
{

    [Indexed(Index = "User")]
    public class User
    {
        public User()
        {
       
        }

        private Guid? userID;
       
        [DocumentId(Name = "UserID")]
        [FieldBridge(typeof(GuidBridge))]
        public virtual Guid? UserID
        {
            get { return userID; }
            set { userID = value; }
        }

        private Guid? applicationID;
        public virtual Guid? ApplicationID
        {
            get { return applicationID; }
            set { applicationID = value; }
        }

        private string userName;
        [Field(Index.Tokenized, Store = Store.No)]
        [Analyzer(typeof(StandardAnalyzer))]
        public virtual string UserName
        {
            get { return userName; }
            set { userName = value; }
        }

        private string loweredUserName;
        [Field(Index.Tokenized, Store = Store.No)]
        [Analyzer(typeof(StandardAnalyzer))]
        public virtual string LoweredUserName
        {
            get { return loweredUserName; }
            set { loweredUserName = value; }
        }

        private string mobileAlias;
        public virtual string MobileAlias
        {
            get { return mobileAlias; }
            set { mobileAlias = value; }
        }

        private bool isAnonymous;
        public virtual bool IsAnonymous
        {
            get { return isAnonymous; }
            set { isAnonymous = value; }
        }

        private DateTime? lastActivityDate;
        public virtual DateTime? LastActivityDate
        {
            get { return lastActivityDate; }
            set { lastActivityDate = value; }
        }
    }
}

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   assembly="NHibernateSearch-Demo"
                   namespace="NHibernateSearch_Demo.Model">

  <class name="User" table="aspnet_Users">
    <id name="UserID" type="guid">
      <generator class="guid"/>
    </id>
    <property name="ApplicationID"/>
    <property name="UserName" length="256" not-null="true"/>
    <property name="LoweredUserName" length="256" not-null="true"/>
    <property name="MobileAlias" length="256" not-null="true"/>
    <property name="IsAnonymous" not-null="true"/>
    <property name="LastActivityDate" not-null="true"/>
  </class>

</hibernate-mapping>

namespace NHibernate.Search.Bridge.Builtin
{
    public class GuidBridge : SimpleBridge
    {
        public override object StringToObject(string stringValue)
        {
            return new System.Guid(stringValue);
        }
    }
}