多对多的实例很多,这里说一个比较简单的例子,而且还是单向引用.. 比如说一个人可以对应多个地址,一个地址可以被多个人所拥有..
这就是对多多的关联关系,
在做多对多的关联的时候,一定要注意,别遗漏 中间表的配置。
下面是Pojo的类:
Person_FK_Many_to_Many:
public class Person_FK_Many_to_Many implements Serializable{
private static final long serialVersionUID = -7132895885951796381L;
private Integer id;
private String name;
private Integer age;
private Set<Address_FK_Many_to_Many> addressFKManyToManieSet = new HashSet<Address_FK_Many_to_Many>();
//getter 和setter方法省略;
}
Address_FK_Many_to_Many:
public class Address_FK_Many_to_Many {
private Integer addressID;
private String addressDetail;
//getter和setter方法省略;
}
下面是Hibernate配置代码:
Person_FK_Many_to_Many.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="pack.java.model.Person_FK_Many_to_Many" table="ZHT_PERSON_FK_MANY_TO_MANY">
<id name="id">
<generator class="identity"/>
</id>
<property name="name" column="NAME"></property>
<property name="age" column="AGE"></property>
<!--
ZHT_PERSON_ADDRESS_MANY_TO_MANY 这个set中的table,是指映射到数据库中的中间表; 用来存储personID 和 AddressID。
-->
<set name="addressFKManyToManieSet" lazy="false" table="ZHT_PERSON_ADDRESS_MANY_TO_MANY" inverse="false" cascade="all">
<key column="id" not-null="false" ></key>
<many-to-many column="addressID" class="pack.java.model.Address_FK_Many_to_Many">
</many-to-many>
</set>
</class>
</hibernate-mapping>
Address_FK_Many_to_Many.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="pack.java.model.Address_FK_Many_to_Many" table="ZHT_ADDRESS_FK_MANY_TO_MANY">
<id name="addressID">
<generator class="identity"></generator>
</id>
<property name="addressDetail" column="addressDetail"></property>
</class>
</hibernate-mapping>
然后再Hibernate.cfg.xml中,把刚刚建立的两个*.hbm.xml文件。
<mapping resource="pack/java/model/Address_FK_Many_to_Many.hbm.xml"/>
<mapping resource="pack/java/model/Person_FK_Many_to_Many.hbm.xml"/>最后,就写一个测试类,来测试刚刚配置的单向多对多的关联关系.
package pack.java.test;
import java.util.List;
import java.util.Set;
import org.hibernate.Query;
import org.hibernate.Session;
import pack.java.hibernate.HibernateSessionFactory;
import pack.java.model.Address_FK_Many_to_Many;
import pack.java.model.Person_FK_Many_to_Many;
/**
* 一个人可以对应多个地址，一个地址，也可以对应多个人。
* @author Administrator
*
*/
public class HibernateDemoManyToMany {
private Session getSession(){
Session session = HibernateSessionFactory.getSession();
return session;
}
public static void main(String[] args) {
HibernateDemoManyToMany demoManyToMany = new HibernateDemoManyToMany();
Session session = demoManyToMany.getSession();
//保存；
demoManyToMany.savePerson(session);
//查询;
demoManyToMany.queryPerson(session);
}
private void queryPerson(Session session){
//Person_FK_Many_to_Many personFKManyToMany = (Person_FK_Many_to_Many) session.load(Person_FK_Many_to_Many.class, 1);
String hql = "select p from Person_FK_Many_to_Many p";
Query query = session.createQuery(hql);
List<Person_FK_Many_to_Many> list = query.list();
for(Person_FK_Many_to_Many personFKManyToMany:list){
System.out.println(personFKManyToMany.getId()+","+personFKManyToMany.getName()+","+personFKManyToMany.getAge());
Set<Address_FK_Many_to_Many> addressFKManyToManies = personFKManyToMany.getAddressFKManyToManieSet();
for (Address_FK_Many_to_Many addressFKManyToMany : addressFKManyToManies) {
System.out.println(addressFKManyToMany.getAddressID()+","+addressFKManyToMany.getAddressDetail());
}
}
session.close();
System.out.println(list.get(0).getAddressFKManyToManieSet().size());
}
private void savePerson(Session session){
Person_FK_Many_to_Many fkManyToMany1 = new Person_FK_Many_to_Many();
fkManyToMany1.setAge(22);
fkManyToMany1.setName("ZhouHaiTao");
Person_FK_Many_to_Many fkManyToMany2 = new Person_FK_Many_to_Many();
fkManyToMany2.setAge(23);
fkManyToMany2.setName("ZhangSan");
Address_FK_Many_to_Many addressFKManyToMany1 = new Address_FK_Many_to_Many();
addressFKManyToMany1.setAddressDetail("北京市朝阳区");
Address_FK_Many_to_Many addressFKManyToMany2 = new Address_FK_Many_to_Many();
addressFKManyToMany2.setAddressDetail("深圳市罗湖区");
Address_FK_Many_to_Many addressFKManyToMany3 = new Address_FK_Many_to_Many();
addressFKManyToMany3.setAddressDetail("长沙市雨花区");
fkManyToMany1.getAddressFKManyToManieSet().add(addressFKManyToMany1);
fkManyToMany1.getAddressFKManyToManieSet().add(addressFKManyToMany2);
fkManyToMany2.getAddressFKManyToManieSet().add(addressFKManyToMany2);
fkManyToMany2.getAddressFKManyToManieSet().add(addressFKManyToMany3);
session.beginTransaction().begin();
//保存Peron第一个对象;
session.save(fkManyToMany1);
//保存Person第二个对象;
session.save(fkManyToMany2);
session.beginTransaction().commit();
}
}
控制输出入如下:
1,ZhouHaiTao,22
1,深圳市罗湖区
2,北京市朝阳区
2,ZhangSan,23
1,深圳市罗湖区
3,长沙市雨花区
