<hibernate-mapping>

  <class name="my.faq.Topic" table="faq_topic">
    <id name="id" column="ID" type="long" unsaved-value="any">
      <generator class="hilo">
        <param name="table">hibernate_unique_key</param>
        <param name="column">next_faq_topic</param>
      </generator>
    </id>
    <property name="name" column="name" type="string"/>
    <list name="units" cascade="all" table="faq_unit" lazy="true">
      <key column="topic_id"/>
      <index column="index1"/>
      <one-to-many class="my.faq.Unit"/>
    </list>
  </class>

  <class name="my.faq.Unit" table="faq_unit">
    <id name="id" column="ID" type="long" unsaved-value="any">
      <generator class="hilo">
        <param name="table">hibernate_unique_key</param>
        <param name="column">next_faq_unit</param>
      </generator>
    </id>
    <property name="topicId" column="topic_id" type="long"/>
    <property name="index" column="index1" type="int"/>
  </class>

</hibernate-mapping>

Unit firstUnit = new Unit();
Session sess = getNewSession();
Topic topic = sess.open(...);
topic.getUnits().add(firstUnit);
sess.update(topic);

System.out.println(firstUnit.getIndex()); // returns 0

sess.close();

<some other code>

Unit secondUnit = new Unit();
sess = getNewSession();
Topic topic = sess.open(...);
topic.getUnits().add(secondUnit);
sess.update(topic);

System.out.println(secondUnit.getIndex()); // returns also 0!
sess.update(secondUnit); // persists secondUnit with index=0

sess.close();