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 column="addressdetail" type="string"/>
??????? <set name="persons" table="join_nn_sx">
??????????? <key column="addressid"/>
??????????? <many-to-many column="personid" table="person_nn_sx">
??????? <id column="personid" name="personid" type="int">
??????????? <generator 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();
??? }
}