I have two entities User and Exam. The relationship between them is many-to-many since a single User can take many exams and a single Exam is given to many users.

I have a exam persisted in the database and now I want to fetch the exam but not the Users of the exam. So, I have a mapping in my Exam.hbm.xml something like this:

<bag name="Users" access="nosetter.camelcase-underscore" inverse="true" lazy="true" cascade="save-update" table="UserExams" >

<key column="ExamID" />
<many-to-many class="User" column="UserID" />
</bag>


The ExamManager.GetById method fetches the Exam

public static Exam GetById(int id)
{
Exam exam = null;

using (ISession session = sessionFactory.OpenSession())
{
exam = session.Get<Exam>(id);

// initialize the collection
NHibernateUtil.Initialize(exam.Users);

}

return exam;
}

And here is the code that is blowing off:

Exam exam = ExamManager.GetById(55);


foreach (User u in exam.Users)
{

// blows when I try to access the FirstName
Console.WriteLine(u.FirstName);


}


The exception is "Failed to Initialize a Lazy Collection". The inner exception is "Object Reference not set to an instance of an object".

Here is the Exam.cs:

private IList<User> _users = new List<User>();

And the Users property:

public IList<User> Users
{
get {

return new ReadOnlyCollection<User>(_users); }
}


Thanks!

I debugged the application and when I debug it then it does not throw any error. But when I run it then it throws the errors.

I mean in debug mode It does not even go in the catch block.