对引用实体有限制的NHibernate查询

我正在使用Nhibernate和SQL server 2008。

我正在尝试执行以下代码:

        var localization = session.QueryOver<T>()
            .Where(idFilter).AndRestrictionOn(x => x.Language.IETFTag).IsLike(tag + "%").SingleOrDefault();

然而，我在那一行得到一个异常，说nhibernate不能解析属性语言。IETFTag(或类似的东西).

我试过使用JoinQueryOver()，但它抱怨我有多个相关性在FROM子句或类似的奇怪的东西。我只是觉得我做错了什么。我怎样才能做我想做的?

我有以下映射:

internal class LocalizationMapping : ClassMap<Localization>
{
    public LocalizationMapping()
    {
        UseUnionSubclassForInheritanceMapping();
        Id(x => x.Id).GeneratedBy.HiLo("HiLo", "NextHi", "1000");
        References(x => x.Language);
    }
}
internal class LanguageMapping : ClassMap<Language>
{
    public LanguageMapping()
    {
        Id(x => x.Id);
        Map(x => x.DefaultName);
        Map(x => x.IETFTag);
    }
}
internal class ArticleLocalizationMapping : SubclassMap<ArticleLocalization>
{
    public ArticleLocalizationMapping()
    {
        Map(x => x.Name);
        Map(x => x.Description);
        References(x => x.Article);
    }
}

Language language = null;
var localization = session.QueryOver<Localization>()
            .JoinAlias(x => x.Language, () => language)
            .Where(idFilter)
            .AndRestrictionOn(() => language.IETFTag).IsLike(tag, MatchMode.End)
            .SingleOrDefault();