7.3. Unidirectional associations with join tables

7.3.1. one to many

A unidirectional one-to-many association on a join table is much preferred. Notice that by specifying unique="true", we have changed the multiplicity from many-to-many to one-to-many.
<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <set name="addresses" table="PersonAddress">
        <key column="personId"/>
        <many-to-many column="addressId"
            unique="true"
            class="Address"/>
    </set>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
</class>
create table Person ( personId bigint not null primary key )
create table PersonAddress ( personId not null, addressId bigint 
    not null primary key )
create table Address ( addressId bigint not null primary key )