7.4.2. One-to-one

外部キーの双方向一対一関連 は一般的です。 
<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <many-to-one name="address" 
        column="addressId" 
        unique="true"
        not-null="true"/>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
   <one-to-one name="person" 
        property-ref="address"/>
</class>
create table Person ( personId bigint not null primary key, addressId bigint not null unique )
create table Address ( addressId bigint not null primary key )
主キーの双方向一対一関連 は特殊な ID ジェネレータを使います。 
<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <one-to-one name="address"/>
</class>

<class name="Address">
    <id name="id" column="personId">
        <generator class="foreign">
            <param name="property">person</param>
        </generator>
    </id>
    <one-to-one name="person" 
        constrained="true"/>
</class>
create table Person ( personId bigint not null primary key )
create table Address ( personId bigint not null primary key )