<hibernate-mapping package="com.system.dao.hibernate">
    <class name="com.system.Budget" table="BUDGET">
        <id name="id" column="ID" type="long">
            <generator class="sequence">
                <param name="sequence">SEQ_BUDGET</param>
            </generator>
        </id>
        <property name="name" column="NAME" type="string"/>

        <join table="SECURITY_OBJECT" subselect="select OBJECT_ID, SECURITY_GROUP_ID from SECURITY_OBJECT so where so.SECURITY_OBJECT_TYPE_CODE = 'BUDGET'" inverse="true" optional="true">
            <key column="OBJECT_ID"/>
            <many-to-one name="securityGroup" column="SECURITY_GROUP_ID" class="com.system.security.SecurityGroup" lazy="false" update="false" insert="false" cascade="none" />
        </join>
    </class>
</hibernate-mapping>

Budget budget = budgetDao.findById(4L);
budget.getSecurityGroup().setName("the new name");
budgetDao.update(budget);