R – Lazy load nhibernate one-to-one

many-to-many relationships ALWAYS require that you mark one end point of the relation with inverse. In your sepecific example you could use the AddressDetails of Person. e.g.

<bag name="AddressDetails" table="PersonAddressMap" cascade="all" inverse="true">
  <key column="PersonId" />
  <one-to-many class="PersonAddressMap" />
</bag>

As Matthieu says, the only case where you wouldn't want to set inverse = true is where it does not make sense for the child to be responsible for updating itself, such as in the case where the child has no knowledge of its parent.

Lets try a real world, and not at all contrived example:

<class name="SpyMaster" table="SpyMaster" lazy="true">
  <id name="Id">
    <generator class="identity"/>
  </id>
  <property name="Name"/>
  <set name="Spies" table="Spy" cascade="save-update">
    <key column="SpyMasterId"/>
    <one-to-many class="Spy"/>
  </set>
</class>

<class name="Spy" table="Spy" lazy="true">
  <id name="Id">
    <generator class="identity"/>
  </id>
  <property name="Name"/>
</class>

Spymasters can have spies, but spies never know who their spymaster is, because we have not included the many-to-one relationship in the spy class. Also (conveniently) a spy may turn rogue and so does not need to be associated with a spymaster. We can create entities as follows:

var sm = new SpyMaster
{
    Name = "Head of Operation Treadstone"
};
sm.Spies.Add(new Spy
{
    Name = "Bourne",
    //SpyMaster = sm // Can't do this
});
session.Save(sm);

In such a case you would set the FK column to be nullable because the act of saving sm would insert into the SpyMaster table and the Spy table, and only after that would it then update the Spy table to set the FK. In this case, if we were to set inverse = true, the FK would never get updated.