Fluent NHibernate Joined References Ignoring Cascade Rule

I'm using Fluent NHibernate in an attempt to improve testability and maintainability on a web application that is using a legacy database and I'm having some trouble mapping this structure properly:

I have two tables that really represent one entity in the domain, and so I'm using a join to map them as such, and a third table that represents a second entity.

DB Tables:

[eACCT]
    ACCT_开发者_运维问答ID
    ACCT_NAME

[eREPORT_TYPE]
    ACCT_ID
    REPORT_NO

[eREPORT_TYPE_DESC]
    REPORT_NO
    REPORT_TYPE

Entities:

public class Account
{
    public virtual string AccountID { get; set; }
    public virtual string AccountName { get; set; }
    public virtual ReportType ReportType { get; set; }
}

public class ReportType
{
    public virtual int Number { get; set; }
    public virtual string Type { get; set; }
}

Mapping:

    public AccountMap()
    {
        Table("eACCT");
        Id(x => x.AccountID, "ACCT_ID");
        Map(x => x.AccountName, "ACCT_NAME");

        Join("eREPORT_TYPE", m =>
        {
            m.KeyColumn("ACCT_ID");
            m.References(x => x.ReportType)
                .Cascade.None()
                .Column("REPORT_NO");
        });
    }

    public ReportTypeMap()
    {
        Table("eREPORT_TYPE_DESC");
        Id(x => x.Number)
            .Column("REPORT_NO")
            .GeneratedBy.Assigned();
        Map(x => x.Type, "REPORT_TYPE");
    }

This works fine for my Gets, but when I modify Account.ReportType.Number and then SaveOrUpdate() Account, I get the error: 'identifier of an instance of DataTest.Model.ReportType was altered from (old_value) to (new_value)'.

All I want to do is modify Account's reference to ReportType and I thought that by setting the Cascade.None() property on the reference to ReportType, NHibernate wouldn't attempt to save the ReportType instance as well, but I must be misunderstanding how that works. I've tried making ReportType ReadOnly(), making the reference to ReportType ReadOnly(), etc and nothing seems to help.

Any ideas?

---

Finally solved this problem. Turns out I wasn't thinking about this in an NHibernate way. In my mind I had a new ReportType.Number, so that's what I needed to update. In reality, what I needed to do was get the ReportType with the new ReportType.Number and set the Account.ReportType. Doing it this way worked as expected.