如何在流畅的nhibernate中覆盖约定的级联规则

I have two classes

我有两节课

public class Document 
{ 
    public virtual int Id { get; set; } 
    public virtual IList<File> Files { get; set; } 
} 
public class File 
{ 
    public virtual int Id { get; protected set; } 
    public virtual Document Document { get; set; } 
} 
public class Docu