hibernate 多对多映射

//A.hbm.xml
<hibernate-mapping>
    <class name="A" table="a">
        <id name="id" type="long">
            <column name="id" precision="22" scale="0" />
            <generator class="increment"></generator>
        </id>
        <property name="name" type="string">
            <column name="name" length="100" />
        </property>
        
        <set name="items" table="ab" cascade="delete" inverse="true" order-by="a_id" lazy="false">
         <key column="a_id"/>
         <one-to-many class="AB"/>
        </set>
    </class>
</hibernate-mapping>
//B的同理
//Ab.hbm.xml
<hibernate-mapping>
    <class name="AB" table="ab">
        <id name="a_id" type="long">
            <column name="a_id" precision="22" scale="0" />
        </id>
        <id name="b_id" type="long">
            <column name="b_id" precision="22" scale="0" />
        </id>
        
        <many-to-one name="a" class="A" fetch="select" lazy="false">
            <column name="a_id" precision="22" scale="0" />
        </many-to-one> <many-to-one name="b" class="B" fetch="select" lazy="false">
            <column name="b_id" precision="22" scale="0" />
        </many-to-one>
    </class>
</hibernate-mapping>