Linq到复合元素父属性无法解析属性

Question

有这样的映射文件：

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   assembly="NHibernate.Test"
                   namespace="NHibernate.Test.NHSpecificTest.CompositeElement">
  <class name="Parent" table="Parents">
    <id name="ParentId">
      <generator class="hilo" />
    </id>
    <list name="Children" table="Children" inverse="true" cascade="all,delete-orphan">
      <key column="ParentId" />
      <list-index column="Position" />
      <composite-element class="Child">
        <parent name="ParentLink"></parent>
      </composite-element>
    </list>
  </class>
</hibernate-mapping>

使用此类实体

public class Parent
{
    public virtual int ParentId { get; set; }
    public virtual IList<Child> Children { get; set; }
}

public class Child
{
    public virtual Parent ParentLink { get; set; }
}

我无法执行以下查询：

(from p in session.Query<Parent>().SelectMany(x => x.Children)
 select p.ParentLink.ParentId).ToList();

失败，异常Hibernate.QueryException : could not resolve property: ParentLink of: component[]

我做错了什么？