NHibernate一对一映射-不保存完整对象图

我试图让NHibernate在一对一的映射方案中保存完整的对象图。我有以下课程

public class Employee : EntityBase
{
    public virtual string EmployeeNumber { get; set; }
    public virtual Address ResidentialAddress {get; set; }
}

public class Address : EntityBase
{
    public virtual string AddressLine1 { get; set; }
    public virtual string AddressLine2 { get; set; }
    public virtual string Postcode { get; set; }
    public virtual string City { get; set; }
    public virtual string Country { get; set; }
    public virtual Employee Employee { get; set; }
}

我试图在此处使用一对一映射，以便一名员工只有一个居住地址。我的对应关系如下

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Domain" namespace="Domain">
  <class name="Employee">
    <id name="Id" generator="hilo" />
    <property name="EmployeeNumber" length="10" />
    <one-to-one name="ResidentialAddress" class="Address" property-ref="Employee" cascade="all" />    
  </class>
</hibernate-mapping>

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Domain" namespace="Domain">
  <class name="Address">
    <id name="Id" generator="hilo" />
    <property name="AddressLine1"/>
    <property name="AddressLine2" />
    <property name="Postcode" />
    <property name="City" />
    <property name="Country" />

    <many-to-one name="Employee" class="Employee" unique="true" />

  </class>
</hibernate-mapping>

我正在使用以下代码来保存员工对象的实例

using (var transaction = Session.BeginTransaction())
        {
            id = Session.Save(new Employee
            {
                EmployeeNumber = "123456789",
                ResidentialAddress = new Address
                {
                    AddressLine1 = "Address line 1",
                    AddressLine2 = "Address line 2",
                    Postcode = "postcode",
                    City = "city",
                    Country = "country"
                }
            });
            transaction.Commit();
        }

在上述情况下，Address上返回给Employee的外键始终为空。但是，如果我ResidentialAddress在Employee类上更改R属性，以便Employee始终按如下所示正确填充该属性

private Address address;
    public virtual Address ResidentialAddress
    {
        get { return address; }
        set
        {
            address = value;

            if (value != null) value.Employee = this;
        }
    }

这使其完美工作。为什么要设置ResidentialAddress.Employee？我在映射中缺少什么吗？NHibernate是否应该不自动保存完整的对象图（并因此确定适当的外键值）。

上面的工作代码使我担心，因为在从数据库加载实体期间从NHiberante调用它时可能会产生问题。