$ cat Audit.hbm.xml
<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping
>
    <class
        name="Audit"
        table="nm_audit"
    >

        <id
            name="id"
            column="id"
            type="java.lang.Long"
        >
            <generator class="sequence">
                <param name="sequence">nm_audit_sequence</param>
              <!--
                  To add non XDoclet generator parameters, create a file named
                  hibernate-generator-params-Audit.xml
                  containing the additional parameters and place it in your merge dir.
              -->
            </generator>
        </id>

        <property
            name="date"
            type="java.util.Date"
            update="true"
            insert="true"
            column="date"
            not-null="true"
        />

        <many-to-one
            name="user"
            class="User"
            cascade="none"
            outer-join="auto"
            update="true"
            insert="true"
            column="user_id"
            not-null="true"
        />

        <!--
            To add non XDoclet property mappings, create a file named
                hibernate-properties-Audit.xml
            containing the additional properties and place it in your merge dir.
        -->

        <joined-subclass
            name="RecordAudit"
            table="nm_record_audit"
        >
            <key
                column="audit_id"
            />

        <many-to-one
            name="record"
            class="Record"
            cascade="none"
            outer-join="auto"
            update="true"
            insert="true"
            column="record_id"
            not-null="true"
        />

        <joined-subclass
            name="RecordField"
            table="nm_record_field"
        >
            <key
                column="record_audit_id"
            />

        </joined-subclass>

        </joined-subclass>

    </class>

</hibernate-mapping>




nm=# \d nm_audit
                 Table "public.nm_audit"
  Column   |            Type             | Modifiers
---------------+-----------------------------+-----------
id        | bigint                      | not null
date      | timestamp without time zone | not null
user_id   | bigint                      | not null
record_id | bigint                      |
Indexes:
    "nm_audit_pkey" PRIMARY KEY, btree (id)
Foreign-key constraints:
    "fkd072815bb2993bcd" FOREIGN KEY (record_id) REFERENCES nm_record(id)
    "fkd072815be6b9eb4d" FOREIGN KEY (user_id) REFERENCES nm_user(id)




nm=# \d nm_record_audit
Table "public.nm_record_audit"
  Column   |  Type  | Modifiers
---------------+--------+-----------
audit_id  | bigint | not null
record_id | bigint | not null
Indexes:
    "nm_record_audit_pkey" PRIMARY KEY, btree (audit_id)
Foreign-key constraints:
    "fka118d2d9b2993bcd" FOREIGN KEY (record_id) REFERENCES nm_record(id)
    "fka118d2d939753cc7" FOREIGN KEY (audit_id) REFERENCES nm_audit(id)





nm=# \d nm_record_field
        Table "public.nm_record_field"
     Column      |  Type  | Modifiers
---------------------+--------+-----------
record_audit_id | bigint | not null
Indexes:
    "nm_record_field_pkey" PRIMARY KEY, btree (record_audit_id)
Foreign-key constraints:
    "fk60d9217415dc360c" FOREIGN KEY (record_audit_id) REFERENCES nm_record_audit(audit_id)