NHibernate:筛选包含联接的子集合

我有以下映射文件：

<?xml version="1.0" encoding="utf-8"?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   assembly="MyAssembly" namespace="EntityNamespace">
  <class name="Server" xmlns="urn:nhibernate-mapping-2.2" table="tblServer" >
    <id name="Id" type="int">
      <generator class="native" />
    </id>
    <bag name="Services" cascade="all" inverse="true" lazy="true">
           <key column="Id" />
      <one-to-many class="Service" />
      <filter name="currentServices" condition=":currentDate BETWEEN DtStart AND DtEnd" />
    </bag>

  </class>

  <filter-def name="currentServices">
    <filter-param name="currentDate" type="System.DateTime"/>
  </filter-def>
</hibernate-mapping>

其中，服务器id和日期是示例。问题是为筛选器生成的sql使用了错误的表别名，应改为：

BETWEEN service0_1_.DtStart AND service0_1_.DtEnd

我做错了什么？有更好的方法吗

IList<Server> servers;
using (var tx = Session.BeginTransaction())
{
    Session.EnableFilter("currentServices")
        .SetParameter("currentDate", DateTime.Now);
    servers = Session.CreateCriteria<Server>()
        .List<Server>();
    tx.Commit();
}

SELECT service0_.server_id as server2_1_,
       service0_.id        as id1_,
       service0_1_.DtStart as DtStart256_0_,
       service0_1_.DtEnd   as DtEnd256_0_
FROM   tblTfopt valueadded0_
       inner join tblServiceOptMatrix service0_1_
         on service0_.id = service0_1_.ServiceOptID
WHERE  '2010-01-07T14:58:09.00' /* @p0 */ 
    BETWEEN service0_.DtStart AND service0_.DtEnd
       and service0_.server_id = 993 /* @p1 */

BETWEEN service0_1_.DtStart AND service0_1_.DtEnd