流利的NHibernate多对多映射可保存所有项目，但不会获取所有项目

Question

I have a Course table:

CourseID    Name
--------------------
1           Course 1
2           Course 2
3           Course 3

A Quiz table:

QuizID    CourseID    Name
----------------------------
1         1           Quiz 1
2         1           Quiz 2
3         1           Quiz 3

A Question table:

QuestionID    Text
-----------------------------
1             What is foo?
2             What is bar?
3             What is foobar?

And a QuizQuestion table:

QuizID    QuestionID
--------------------
1         1
1         2
2         2
2         3

The front-end for managing this data looks like this (I wish I had more say in how it has to look):

The UI probably doesn't matter, but hopefully it gives you a better idea. I'm using Fluent NHibernate with the following mappings:

public class CourseMapOverride : IAutoMappingOverride<Course>
{
    public void Override( AutoMapping<Course> mapping )
    {
        mapping.Table( "Course" );

        mapping.Id( x => x.Id ).Column( "CourseID" );

        mapping.HasMany( x => x.Exams )
               .KeyColumn( "CourseID" )
               .Cascade.All()
               .Inverse();
    }
}

public class ExamMapOverride : IAutoMappingOverride<Exam>
{
    public void Override( AutoMapping<Exam> mapping )
    {
        mapping.Table( "Quiz" );

        mapping.Id( x => x.Id ).Column( "QuizID" );

        mapping.References( x => x.Course ).Column( "CourseID" );

        mapping.HasManyToMany( x => x.Questions )
               .Table( "QuizQuestion" )
               .ParentKeyColumn( "QuizID" )
               .ChildKeyColumn( "QuestionID" )
               .Cascade.All();
    }
}

public class QuestionMapOverride : IAutoMappingOverride<Question>
{
    public void Override( AutoMapping<Question> mapping )
    {
        mapping.Table( "Question" );

        mapping.Id( x => x.Id ).Column( "QuestionID" );

        mapping.HasManyToMany( x => x.Exams )
               .Table( "QuizQuestion" )
               .ParentKeyColumn( "QuestionID" )
               .ChildKeyColumn( "QuizID" )
               .Cascade.All()
               .Inverse();
    }
}

Yes, the Quiz table maps to the Exam class for some reason. When the form is posted, I look at each checkbox, determine whether the QuizQuestion already exists, and insert a new row if it doesn't. This part is working correctly, but here is the code anyways:

public void UpdateCourse( EditCourseModel model )
{
    var course = CourseRepository.Get( model.CourseID );

    course.Name = model.Name;

    foreach ( var examQuestionModel in model.Questions
                                            .SelectMany( q => q.ExamQuestions )
                                            .Where( eq => eq.Selected ) )
    {
        UpdateExamQuestion( course, examQuestionModel );
    }
}

private void UpdateExamQuestion( Course course, ExamQuestionModel model )
{
    var exam = course.Exams.First( e => e.Id == model.ExamID );

    if ( exam.Questions.Any( q => q.Id == model.QuestionID ) )
    {
        // it already exists
        return;
    }

    var question = QuestionRepository.Get( model.QuestionID );

    exam.Questions.Add( question );

    question.Exams.Add( exam );
}

Say, for instance, I select the following checkboxes:

After I post the form, I can verify the new row was added by looking at the QuizQuestion table in the database:

QuizID    QuestionID
--------------------
1         1
1         2
2         2
2         3
3         1
3         3

For some reason, however, the new row is not part of the data set that is displayed on the following page. After a save/commit/flush/redirect, the next page looks exactly like it did before:

It's not a problem with the view, because when I pause the debugger inside of the foreach loop in the GetQuestionModel method (below), exam.Questions is empty:

public CourseModel GetCourseModel( int courseID )
{
    var course = CourseRepository.Get( courseID );

    var questions = QuestionRepository.GetAll()
                                      .Select( q => GetQuestionModel( course.Exams, q ) )
                                      .ToList();

    return new CourseModel
               {
                   CourseID = course.ID,
                   Name = course.Name,
                   Questions = questions,
               };
}

public QuestionModel GetQuestionModel( IEnumerable<Exam> exams, Question question )
{
    var model = new QuestionModel
                    {
                        QuestionID = question.ID,
                        Text = question.Text,
                        ExamQuestions = new List<ExamQuestionModel>(),
                    };

    foreach ( var exam in exams )
    {
        // exam.Questions is empty when exam.ID is 3
        var examQuestionIDs = exam.Questions.Select( q => q.ID );

        model.ExamQuestions.Add( new ExamQuestionModel
                                     {
                                         ExamID = exam.ID,
                                         QuestionID = question.ID,
                                         Selected = examQuestionIDs.Contains( question.ID ),
                                     } );
    }

    return model;
}

Here's the GetAll method from the Repository class:

public virtual IQueryable<T> GetAll()
{
    return LinqExtensionMethods.Query<T>( this.Session );
}

The strangest part of this whole thing is if I rebuild the solution the problem fixes itself. It has to be a rebuild though, or a code change followed by a build.

This is driving me bonkers. What am I doing wrong?

EDIT

I suspected this had something to do with NHibernate caching, so I applied this mapping convention . No luck however.

EDIT 2

As I said earlier, a rebuild somehow refreshes the data. I was able to add several questions to Quiz with ID of 3, and after rebuilding they appeared in the list. Then I deleted all the rows in the join table, but the questions are still in the list. I'm even more convinced now that this might be a problem with NHibernate caching.

Answer 1

I finally found the problem:

var questions = QuestionRepository.GetAll()
                                  .Select( q => GetQuestionModel( course.Exams, q ) )
                                  .ToList();

Should be:

var questions = QuestionRepository.GetAll()
                                  .ToList()
                                  .Select( q => GetQuestionModel( course.Exams, q ) )
                                  .ToList();

It seems like every time I have a frustratingly difficult problem with NHibernate it's because I'm missing a call to ToList somewhere. It's starting to really get on my nerves.