public class User {

public User() {
   }

public int UserId
   {
      get { return userId; }
      set { userId = value; }
   }

public int Name
   {
      get { return name; }
      set { name = value; }
   }

public IDictionary Groups
   {
      get { return groups; }
      set { groups = value; }
   }

private int userId;
   private string name;
   private IDictionary groups = new Hashtable();

} //class User

public class Group {

public Group() {
   }

public int GroupId
   {
      get { return groupId; }
      set { groupId = value; }
   }

public int Name
   {
      get { return name; }
      set { name = value; }
   }

public int Description
   {
      get { return description; }
      set { description = value; }
   }

public IDictionary Users
   {
      get { return users; }
      set { users = value; }
   }

private int groupId;
   private string name;
   private IDictionary users = new Hashtable();

} //class Group

public TestCreate() {
   User user1 = new User();
   user1.Name = "test1";
   User user2 = new User();
   user2.Name = "test2";

Group group1 = new Group();
   group1.Name = "group1"; 
   Group group2 = new Group();
   group2.Name = "group2";

user1.Groups.Add( group2, group2 );
   user2.Groups.Add( group1. group1 );
   group1.Users.Add( user2, user2 );
   group2.Users.Add( user1, user1 );

ITransactioin trans = null;
   try {
      trans = session.BeginTransaction();

Session.Save( user1 );
      Session.Save( user2 );
      Session.Save( group1 );
      Session.Save( group2 );

trans.Commit();
   }
   catch ( Exception e ) {
      if ( trans != null ) trans.Rollback();
      throw e;
   }
   finally {
      session.Close();
   }
}