nhibernate parent/child one-to-one mapping - nhibernate

Question

I have two classes:
public class Code
{
public virtual Guid CodeId { get; set; }
public virtual string CodeValue { get; set; }
public virtual Guid EntryId { get; set; }
}
public class Entry
{
public virtual Guid EntryId { get; set; }
public virtual string FirstName { get; set; }
public virtual string LastName { get; set; }
public virtual string Address { get; set; }
public virtual string Address2 { get; set; }
public virtual string City { get; set; }
public virtual string State { get; set; }
public virtual string Zip { get; set; }
public virtual string Email { get; set; }
public virtual string Phone { get; set; }
public virtual string IpAddress { get; set; }
public virtual DateTime BirthDate { get; set; }
public virtual DateTime Created { get; set; }
public virtual bool OptIn { get; set; }
public virtual Code Code { get; set; }
}
I want nhibernate to automatically load/save the Code child property of the Entry object (which can be null and is linked by a foreign key "EntryId" in the Codes table), but I cannot figure out the mapping. The documentation at hibernate.org isn't loading for me right now, so could someone point me in the right direction with the mappings below?
<class name="Code" table="Codes">
<id name="CodeId">
<generator class="guid.comb"/>
</id>
<property name="CodeValue" />
<property name="EntryId"
</class>
<class name="Entry" table="Entries">
<id name="EntryId">
<generator class="guid.comb"/>
</id>
<property name="FirstName" />
<property name="LastName" />
<property name="Address" />
<property name="Address2" />
<property name="City" />
<property name="State" />
<property name="Zip" />
<property name="Email" />
<property name="Phone" />
<property name="BirthDate" />
<property name="OptIn" />
<property name="IpAddress" />
<property name="Created" />
</class>

Answer 1

I believe this article describes the possibilities very well:
http://ayende.com/Blog/archive/2009/04/19/nhibernate-mapping-ltone-to-onegt.aspx
You just don't need to "simulate" the bidirectionality, but that's easy to leave out.