如何关闭NHibernate的自动(脏检查)更新行为？

public class MyClassMap : ClassMap<MyClass>
{
    public MyClassMap()
    {
        Id(x => x.Id);
        Map(x => x.PropertyName).ReadOnly();
    }
}

public class MyClassMap : ClassMap<MyClass>
{
    public MyClassMap()
    {
        Id(x => x.Id);
        Map(x => x.PropertyName);
        DynamicUpdate();
    }
}

session.Lock(entity, LockMode.None);