Fluent NHibernate - IndexOutOfRange

I've read all the posts and know that IndexOutOfRange usually happens because a column is being referenced twice. But I don't see how that's happening based on my mappings. With SHOW_SQL true in the config, I see an Insert into the Events table and then an IndexOutOfRangeException that refers to the RadioButtonQuestions table. I can't see the SQL it's trying to use that generates the exception. I tried using AutoMapping and have now switched to full ClassMap for these two classes to try to narrow down the problem.

public class RadioButtonQuestion : Entity
{
    [Required]
    public virtual Event Event { get; protected internal set; }

    [Required]
    public virtual string GroupIntroText { get; set; }
}

public class Event : Entity
{
    [Required]
    public virtual string Title { get; set; }

    [Required]
    public virtual DateTime EventDate { get; set; }

    public virtual IList<RadioButtonQuestions> RadioButtonQuestions { get; protected internal set; }
}




public class RadioButtonQuestionMap : ClassMap<RadioButtonQuestion>
{
    public RadioButtonQuestionMap()
    {
        Table("RadioButtonQuestions");

        Id(x => x.Id).Column("RadioButtonQuestionId").GeneratedBy.Identity();

        Map(x => x.GroupIntroText);
        References(x => x.Event).Not.Nullable();
    }
}


public class EventMap : ClassMap<Event>
{
    public EventMap()
    {
        Id(x => x.Id).Column("EventId").GeneratedBy.Identity();
        Map(x => x.EventDate);
        Map(x => x.Title);
        HasMany(x => x.RadioButtonQuestions).AsList(x => x.Column("ListIndex")).KeyColumn("EventId").Not.Inverse().Cascade.AllDeleteOrphan().Not.KeyNullable();
    }
}

The generated SQL looks correct:

create table Events (
    EventId INT IDENTITY NOT NULL,
   EventDate DATETIME not null,
   Title NVARCHAR(255) not null,
   primary key (EventId)
)

create table RadioButtonQuestions (
    RadioButtonQuestionId INT IDENTITY NOT NULL,
   GroupIntroText NVARCHAR(255) not null,
   EventId INT not null,
   ListIndex INT null,
   primary key (RadioButtonQuestionId)
)

This is using NH 3.3.0.4000 and FNH 1.3.0.727. When I try to save a new Event (with a RadioButtonQuestion attached) I see

NHibernate: INSERT INTO Events (EventDate, Title) VALUES (@p0, @p1);@p0 = 5/21/2012 12:32:11 PM [Type: DateTime (0)], @p1 = 'My Test Event' [Type: String (0)] NHibernate: select @@IDENTITY

Events.Tests.Events.Tasks.EventTasksTests.CanCreateEvent: NHibernate.PropertyValueException : Error dehydrating property value for Events.Domain.RadioButtonQuestion._Events.Domain.Event.RadioButtonQuestionsIndexBackref ----> System.IndexOutOfRangeException : An SqlCeParameter with ParameterIndex '3' is not contained by this SqlCeParameterCollection.

So if a column really is being referenced twice, what's the problem with my FNH config that's causing that behavior? I'm trying for a bidirection relationship (One Event Has Many Radio Button Questions) with ordering (I'll maintain it since NH won't in a bidir relationship, from what I've read). FWIW I also tried this as a unidirectional relationship by removing the Event from RadioButtonQuestion and it still caused the same exception.

You have a bidirectional association, so one side should be marked as Inverse() and that can only be the RadioButtonQuestions collection. If you want the collection to be the owner, you have to remove the reference to the event in your RadioButtonQuestion class.

Additionally, the EventId column in the table RadioButtonQuestions is not nullable, which can cause problems, if the collection mapping is not inverse. See the note in the documentation.