I usually post things of moderate difficulty, let us see if you can not only figure this one out, but where that bug exists.

Given the following class & mapping:

public class User
{
    public virtual string Username { get; set; }
    public virtual ICollection<string> AllowedPaths { get; set; }

    public User()
    {
        AllowedPaths = new HashSet<string>();
    }
}

<class name="User"
       table="Users">

    <id name="Username">
        <generator class="assigned"/>
    </id>
    <set name="AllowedPaths" table="UsersAllowPaths">
        <key column="`User`" not-null="true"/>
        <element column="Path" type="System.String" not-null="true"/>
    </set>
</class>

I have the following code:

public class Program
{
    public static void Main()
    {
        Configuration configuration = new Configuration().Configure("nhibernate.config");
        ISessionFactory sessionFactory = configuration.BuildSessionFactory();
        new SchemaExport(configuration).Create(true, true);


        using (ISession s = sessionFactory.OpenSession())
        using (ITransaction tx = s.BeginTransaction())
        {
            s.Save(new User
            {
                Username = "ayende",
                AllowedPaths = {"/users", "/meetings"}
            });

            tx.Commit();
        }

        using (ISession s = sessionFactory.OpenSession())
        using (ITransaction tx = s.BeginTransaction())
        {
            var user = s.Get<User>("Ayende");
            Console.WriteLine("Found user {0}", user.Username);
            Console.WriteLine("Allowed paths:");
            foreach (string allowedPath in user.AllowedPaths)
            {
                Console.WriteLine("\t{0}", allowedPath);
            }

            tx.Commit();
        }
    }
}

First, and without running the code!

• What is the expected output?
• Am I doing something wrong here?

Then, run the code, and answer them again.

You can download the project here: http://github.com/ayende/NHibernate-Challanges, sub folder TrickyBug