多对多连接表双向关联

多对多连接表双向关联时：只能有一端的<set>放入属性inverse="true",之后Session.save()时，首先保存哪个端POJO均可，当另一端的POJO必须调用saveOrUpdate()进行相应的链接和连接表的更新。

示例：

一个Person可以有多个Address，一个Address可以有多个Person。利用连接表进行双向链接：

数据库表：
CREATE TABLE `address_nn_sx` (
 `addressid` int(11) NOT NULL auto_increment,
 `addressdetail` varchar(255) default NULL,
 PRIMARY KEY (`addressid`)
) ENGINE=InnoDB DEFAULT CHARSET=gbk;
 
CREATE TABLE `person_nn_sx` (
 `personid` int(11) NOT NULL auto_increment,
 `name` varchar(255) default NULL,
 `age` int(11) default NULL,
 PRIMARY KEY (`personid`)
) ENGINE=InnoDB DEFAULT CHARSET=gbk;
 
CREATE TABLE `join_nn_sx` (
 `addressid` int(11) NOT NULL,
  `personid` int(11) NOT NULL,
  PRIMARY KEY (`personid`,`addressid`),
  KEY `FK6EBBC5EF6C600921` (`personid`),
  KEY `FK6EBBC5EF2A92FF3D` (`addressid`),
  CONSTRAINT `FK6EBBC5EF2A92FF3D` FOREIGN KEY (`addressid`) REFERENCES `address_nn_sx` (`addressid`),
  CONSTRAINT `FK6EBBC5EF6C600921` FOREIGN KEY (`personid`) REFERENCES `person_nn_sx` (`personid`)
) ENGINE=InnoDB DEFAULT CHARSET=gbk;
 

POJO（省去getter，setter）:

 
public class Personnn_sx {
 
 private int personid;
 
 private String name;
 
 private int age;
 
 private Set addresses=new HashSet();
 
 
public class Addressnn_sx {
 
 private int addressid;
 
 private String addressdetail;
 
 private Set persons = new HashSet();
 

hbm.xml:

<hibernate-mapping>
    <class name="com.Addressnnsx" table="address_nn_sx">
        <id column="addressid" name="addressid" type="int">
            <generator class="identity"/>
        </id>
        <property name="addressdetail" column="addressdetail" type="string"/>
        <set name="persons" table="join_nn_sx">
            <key column="addressid"/>
            <many-to-many column="personid" class="com.Personnnsx"/>
        </set>
    </class>
</hibernate-mapping>

<hibernate-mapping>
    <class name="com.Personnnsx" table="person_nn_sx">
        <id column="personid" name="personid" type="int">
            <generator class="identity"/>
        </id>
        <property name="name" column="name" type="string"/>
        <property name="age" column="age" type="int"/>

        <set table="join_nn_sx"
        name="addresses" cascade="all" inverse="true">
            <key column="personid"/>
            <many-to-many class="com.Addressnnsx"
             column="addressid"/>
        </set>
    </class>
</hibernate-mapping>

Test Main:

public class Test_nn_sx {
    public static void main(String args[]){
        Addressnnsx add1=new Addressnnsx();
         Addressnnsx add2=new Addressnnsx();
         Personnnsx p1=new Personnnsx();
         Personnnsx p2=new Personnnsx();
         add1.setAddressdetail("郑州市经三路");
         add2.setAddressdetail("合肥市宿州路");
         p1.setName("wang");
         p1.setAge(30);
         p2.setName("zhang");
         p2.setAge(22);

         add1.getPersons().add(p1);
         add2.getPersons().add(p1);
         add2.getPersons().add(p2);
         p1.getAddresses().add(add1);
         p1.getAddresses().add(add2);
         p2.getAddresses().add(add2);
        
         Session session= HibernateUtil.getSession();
         Transaction tx=session.beginTransaction();
         session.save(add1);
         session.save(add2);
         session.saveOrUpdate(p1);
         session.saveOrUpdate(p2);

         //session.save(p1);
         //session.save(p2);
         //session.saveOrUpdate(add1); //上面的save()已经对相应的address进行插入操作，故这里必须检查相应的表是否需要更新再保存
         //session.saveOrUpdate(add2);
         tx.commit();
         HibernateUtil.closeSession();
    }
}