ISession session = Pcms.Classes.Base.NHibernateHelper.SessionFactory.OpenSession();
            ITransaction tx = null;
            IList objList= null;
            objList.Add("1");
            try
            {
                tx = session.BeginTransaction();
                Pcms.Classes.Data.Group objGroup = new Pcms.Classes.Data.Group();
                objGroup.GroupID = 1;
                objGroup.UserID = objList;
                session.Save(objGroup);
                tx.Commit();
            }
            catch (HibernateException eeeee)
            {
                if (tx != null) tx.Rollback();
                throw eeeee;
            }
            finally
            {
                session.Close();

// group class

using System;
using System.Collections;
using System.Text;
using NHibernate.Mapping.Attributes;
using NHibernate;
using NHibernate.Cfg; 

namespace Pcms.Classes.Data
{
    [Class(Table = "[Group]")]
    public class Group
    {
        private int _groupID;
        private string _name;
        private IList _userID;

        [Id(0, Name = "GroupID", Type = "Int32", UnsavedValue = "0")]
        [Generator(1, Class = "identity")]
        public virtual int GroupID
        {
            get { return _groupID;}
            set { _groupID = value;}
        }

        [Property(Type = "AnsiString", NotNull = true, Length = 50)]
        public virtual string Name
        {
            get { return _name; }
            set { _name = value; }
        }

        [Set(0, Name = "UserID", Table = "UserGroup", Lazy = true, Cascade = CascadeStyle.SaveUpdate)]
        [Key(1, Column = "UserID")]
        [ManyToMany(2, Class = "Pcms.Classes.Data.User,Pcms", Column = "GroupID")]
        public virtual IList UserID
        {
            get { return _userID; }
            set { _userID = value; }
        }
    }
}