Fluent NHibernate-HasManyToMany NHibernate.MappingException:

我是一名NHibernate新手，尝试使用Fluent NHibernat配置现有数据库。问题在于多对多映射，在本例中由图书馆和书籍表示。我想这应该是非常基本的东西，但我得到了以下例外：

FluentNHibernate.Cfg.FluentConfigurationException: An invalid or incomplete configuration was used while creating a SessionFactory. Check PotentialReasons collection, and InnerException for more detail.
 ---> NHibernate.MappingException: Repeated column in mapping for collection: MvcNhibernatePoc.Models.Book.Libraries column: BookId

数据库的结构不应该改变，看起来像：

Table **Book**
BookId (int)
BookName (varchar(255))
Table **Library**
LibraryId (int)
LibraryName (varchar(255))
Table **Book_Library**
Id (int)
BookId (int)
LibraryId (int)

基于此，我创建了以下域类：

public class Library
    {
        public virtual int LibraryId { get; set; }
        public virtual string Name { get; set; }
        public virtual IList<Book> Books { get; set; }
        public Library()
        {
            Books = new List<Book>();
        }
    }

public class Book
{
    public virtual int BookId { get; set; }
    public virtual string Name { get; set; }
    public virtual IList<Library> Libraries { get; set; }
    public Book()
    {
        Libraries = new List<Library>();
    }
}

映射：

public class LibraryMap : ClassMap<Library>
{
    public LibraryMap()
    {
        Table("Library");
        Id(l => l.LibraryId).Column("LibraryId");
        Map(l => l.Name).Column("LibraryName");
        HasManyToMany<Book>(l => l.Books)
            .Table("Book_Library")
            .ParentKeyColumn("LibraryId")
            .ChildKeyColumn("LibraryId")
            .Cascade.SaveUpdate();
    }
}
public class BookMap : ClassMap<Book>
{
    public BookMap()
    {
        Table("Book");
        Id(b => b.BookId).Column("BookId");
        Map(b => b.Name).Column("BookName");
        HasManyToMany<Library>(b => b.Libraries)
            .Table("Book_Library")
            .ParentKeyColumn("BookId")
            .ChildKeyColumn("BookId")
            .Cascade.SaveUpdate()
            .Inverse();
    }
}

Fluent配置：

Fluently.Configure()
            .Database(MsSqlConfiguration.MsSql2008.ConnectionString(conString).ShowSql)
            .Mappings(m => m.FluentMappings
            .AddFromAssemblyOf<Library>())
            .BuildSessionFactory();

最后是我失败的测试代码：

var library = new Library { LibraryId = 1, Name = "Alexandria library"};
var book = new Book { BookId = 1, Name = "Pyramids for dummies" };
library.Books.Add(book);
book.Libraries.Add(library);
using (var session = NHibernateHelper.OpenSession())
{
    using (var transaction = session.BeginTransaction())
    {
        session.Save(library);
        session.Flush();
        transaction.Commit();
        Console.WriteLine("Saved library " + library.Name);
    }
}

        .ParentKeyColumn("BookId")
        .ChildKeyColumn("BookId")
        .ParentKeyColumn("LibraryId")
        .ChildKeyColumn("LibraryId")

        // BookMap
        .ParentKeyColumn("BookId")
        .ChildKeyColumn("LibraryId")
        // LibraryMap
        .ParentKeyColumn("LibraryId")
        .ChildKeyColumn("BookId")