NHibernate exception: could not initialize a colle

Question

I am puzzled and frustrated by an exception I'm getting via NHibernate. I apologize for the length of this post, but I've tried to include an appropriate level of detail to explain the issue well enough to get some help!

Here's the facts:

• I have a Person class which contains a property BillingManager, which is also a Person type. I map this as an FNH "Reference".
• I have an ExpenseReport class which contains a property SubmittedBy, which is a Person type. I map this as an FNH "Reference".
• I have a BillableTime class which contains a property Person, which is a Person type. I map this as an FNH "Reference".
• Person contains a collection (IList) of ExpenseReport types (property ExpenseReports)
• Person contains a collection (IList) of BilledTime types (property Time)

(See classes and mappings at bottom of post.)

All was cool until I added the IList<BilledTime> Time collection to Person. Now, when I try to access _person.Time, I get an exception:

The code:

// Get billable hours
if (_person.Time == null || 
    _person.Time.Count(x => x.Project.ProjectId == project.ProjectId) == 0)
{
    // No billable time for this project
    billableHours = Enumerable.Repeat(0F, 14).ToArray();
}

The exception:

could not initialize a collection: 
[MyApp.Business.Person.Time#211d3567-6e20-4220-a15c-74f8784fe47a]
[SQL: SELECT 
time0_.BillingManager_id as BillingM8_1_, 
time0_.Id as Id1_, 
time0_.Id as Id1_0_, 
time0_.ReadOnly as ReadOnly1_0_, 
time0_.DailyHours as DailyHours1_0_, 
time0_.Week_id as Week4_1_0_, 
time0_.Person_id as Person5_1_0_, 
time0_.Project_id as Project6_1_0_, 
time0_.Invoice_id as Invoice7_1_0_ 
FROM [BillableTime] time0_ 
WHERE time0_.BillingManager_id=?]

It's true that BillingManager_id is an invalid column name, it doesn't exist in the BillableTime table. However, I don't understand why NHB has created this SQL... doesn't make sense to me. I have seen this "Invalid column name" exception a lot when searching for a solution, but nothing seems to work. Even more confusing: like BilledTime, the ExpenseReport type also contains a reference to Person and it works perfectly.

One thing I was able to figure out is that if I remove the BillingManager reference from the Person mapping (References(p => p.BillingManager)), the exception goes away and things seem to work (with respect to BillableTime; it of course breaks the BillingManager persistence). Now it seems like there is some "self-reference" problem, since the Person.BillingManager property is itself a reference to a Person.

Any idea what is going on here? I'm at a loss...

Thanks.

=== Classes & Mappings ===

public class Person
{
    public virtual string LastName { get; set; }
    public virtual string FirstName { get; set; }

    public virtual Person BillingManager { get; set; }

    public virtual IList<ExpenseReport> ExpenseReports { get; set; }
    public virtual IList<BillableTime> Time { get; set; }
}


public class PersonMapping : ClassMap<Person> 
{        
    public PersonMapping()
    {
        Id(p => p.UserId).GeneratedBy.Assigned();
        Map(p => p.LastName).Not.Nullable();
        Map(p => p.FirstName).Not.Nullable();

        References(p => p.BillingManager);

        HasMany(p => p.ExpenseReports).Cascade.AllDeleteOrphan();
        HasMany(p => p.Time).Cascade.AllDeleteOrphan(); 
    }
}

public class BillableTime
{
    public virtual int Id { get; private set; }
    public virtual Week Week { get; set; }
    public virtual Person Person { get; set; }
    public virtual Project Project { get; set; }
    public virtual float[] DailyHours { get; set; }
    public virtual Invoice Invoice { get; set; }
    public virtual bool ReadOnly { get; set; }
}       

public class BillableTimeMapping : ClassMap<BillableTime>
{
    public BillableTimeMapping()
    {
        Id(x => x.Id);
        References(x => x.Week);
        References(x => x.Person);
        References(x => x.Project);
        References(x => x.Invoice);
        Map(x => x.ReadOnly).Not.Nullable().Default("0");
        Map(x => x.DailyHours).Length(28);  
    }
}


public class ExpenseReport
{
    public virtual long Id { get; set; }        
    public virtual Person SubmittedBy { get; set; }             
}

Answer 1

the following line should solve the issue, but i' dont know exactly why it is happening. if i have the spare time i will investigate.

HasMany(p => p.Time).Cascade.AllDeleteOrphan().KeyColumn("Person_Id");