如何使用Fluent NHibernate和SchemaUpdate.Execute()索引外键？

public class ProductMap : ClassMap<Product>
{
    public ProductMap()
    {
        Id(x => x.Id);
        Map(x => x.Name);
        Map(x => x.Price);
        References(x => x.Category).Column("CategoryId").Index("IX_Product_CategoryId");
    }
}

public class NHibernateConfig
{
    public static ISessionFactory CreateSessionFactory()
    {
        var configuration = Fluently.Configure()
            .Database(MsSqlConfiguration.MsSql2012.ConnectionString(c => c.FromConnectionStringWithKey("MyConnectionString")))
            .Mappings(m => m.FluentMappings.AddFromAssemblyOf<ProductMap>())
            .ExposeConfiguration(cfg => new SchemaUpdate(cfg).Execute(false, true))
            .BuildConfiguration();

        return configuration.BuildSessionFactory();
    }
}

var sessionFactory = NHibernateConfig.CreateSessionFactory();

using (var session = sessionFactory.OpenSession())
{
    using (var transaction = session.BeginTransaction())
    {
        var product = new Product { Name = "Product 1", Price = 100, Category = new Category { Name = "Category 1" } };
        session.Save(product);
        transaction.Commit();
    }
}