我如何在nhibernate建立一对一的关系?(当前不返回外部对象)

我有一个用户,其中一些是雇员。这是一对一的关系,并非所有用户都是员工。

当我得到一个用户时,它似乎没有带回员工信息,只是将其标记为空。我本以为我已经了解了nhibernate,但我试过在映射文件上使用这么多属性,但没有成功。关于我所做的事情有什么不正确的想法或建议吗?

public class User
    {
        public virtual int UserID { get; set; }
        public virtual string Username { get; set; }
        public virtual string Title { get; set; }
        public virtual string Forename { get; set; }
        public virtual string Surname { get; set; }

        public virtual Employee Employee { get; set; }
    }

用户映射:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   assembly="Portal.Core"
                   namespace="Portal.Core.Data.Database">

  <class name="User" table="[Users]">
    <id name="UserID">
      <generator class="identity" />
    </id>
    <property name="Username" not-null="true" length="50" />
    <property name="Title" length="10" />
    <property name="Forename" length="50" />
    <property name="Surname" length="50" />

    <one-to-one name="Employee" class="Employee" fetch="select" lazy="false" foreign-key="EmployeeID" />


  </class>

</hibernate-mapping>

员工类别:

public class Employee
    {
        public virtual int EmployeeID { get; set; }
        public virtual string RoomNumber { get; set; }
        public virtual string JobTitle { get; set; }
        public virtual User User { get; set; }
    }

员工映射:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   assembly="Portal.Core"
                   namespace="Portal.Core.Data.Database">

  <class name="Employee" table="[Employees]">
    <id name="EmployeeID">
      <generator class="identity" />
    </id>
    <many-to-one name="User" unique="true" column="UserID" class="User" fetch="select" foreign-key="UserID" ></many-to-one>

    <property name="RoomNumber" length="20" />
    <property name="JobTitle" length="20" />

  </class>

</hibernate-mapping>