业务场景：
剃须刀属于家电，也属于日常用品。这种情况就是多对多关系。
一般会多一张表来表示两张表的关系，三张表如下
category:类别表
item:项目表
category_times：关联表，维护category、item的关系
单向多对多-关键代码：
<!-- table:指定中间表 --> <set name="items" table="CATEGORY_TIMES"> <key> <column name="CATEGORY_ID"></column> </key> <!-- 使用many-to-many指定多对多的关联关系 column：执行Set集合的持久化类在中间表的外键列的名称 --> <many-to-many class="com.shuoeasy.test.Item" column="ITEM_ID"></many-to-many> </set>
单向多对多-详细代码：
Category.java:
package com.shuoeasy.test;
import java.util.HashSet;
import java.util.Set;
public class Category {
private int id;
private String name;
private Set<Item> items = new HashSet<>();
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set<Item> getItems() {
return items;
}
public void setItems(Set<Item> items) {
this.items = items;
}
@Override
public String toString() {
return "Category [id=" + id + ", name=" + name + "]";
}
}Item.java:
package com.shuoeasy.test;
public class Item {
private int id;
private String name;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Item [id=" + id + ", name=" + name + "]";
}
}Category.hbm.xml:
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <!-- Generated 2016-6-25 14:50:51 by Hibernate Tools 3.4.0.CR1 --> <hibernate-mapping> <class name="com.shuoeasy.test.Category" table="CATEGORY"> <id name="id" type="int"> <column name="ID" /> <!-- 指定主键的生成方式 --> <generator class="native" /> </id> <property name="name" type="java.lang.String"> <column name="NAME" /> </property> <!-- table:指定中间表 --> <set name="items" table="CATEGORY_TIMES"> <key> <column name="CATEGORY_ID"></column> </key> <!-- 使用many-to-many指定多对多的关联关系 column：执行Set集合的持久化类在中间表的外键列的名称 --> <many-to-many class="com.shuoeasy.test.Item" column="ITEM_ID"></many-to-many> </set> </class> </hibernate-mapping>
Item.hbm.xml:
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <!-- Generated 2016-6-25 14:50:51 by Hibernate Tools 3.4.0.CR1 --> <hibernate-mapping> <class name="com.shuoeasy.test.Item" table="ITEM"> <id name="id" type="int"> <column name="ID" /> <generator class="native" /> </id> <property name="name" type="java.lang.String"> <column name="NAME" /> </property> </class> </hibernate-mapping>
AppTest.java:
package com.shuoeasy.test;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
/**
* Unit test for simple App.
*/
public class AppTest {
Session session;
SessionFactory sf;
@Before
public void init() {
Configuration conf = new Configuration().configure();
ServiceRegistry sr = new StandardServiceRegistryBuilder().applySettings(conf.getProperties()).build();
sf = conf.buildSessionFactory((org.hibernate.service.ServiceRegistry) sr);
session = sf.openSession();
session.beginTransaction();
System.out.println("init");
}
@After
public void destory() {
session.getTransaction().commit();
session.close();
sf.close();
System.out.println("dectory");
}
/**
* 插入数据
*/
@Test
public void testInsert(){
// 创建对象
Category category1 = new Category();
category1.setName("家电");
Category category2 = new Category();
category2.setName("日常用品");
Item item1 = new Item();
item1.setName("剃须刀");
Item item2 = new Item();
item2.setName("电饭锅");
// 设定关联关系
category1.getItems().add(item1);
category1.getItems().add(item2);
category2.getItems().add(item2);
// 执行保存操作
session.save(category1);
session.save(category2);
session.save(item1);
session.save(item2);
}
/**
* 获取数据-单向多对多
*/
@Test
public void testGet(){
Category category = (Category) session.get(Category.class, 1);
System.out.println(category);
for(Item item : category.getItems()){
System.out.println(item);
}
}
}生成sql:
Hibernate: select category0_.ID as ID1_0_0_, category0_.NAME as NAME2_0_0_ from CATEGORY category0_ where category0_.ID=? Category [id=1, name=家电] Hibernate: select items0_.CATEGORY_ID as CATEGORY1_0_0_, items0_.ITEM_ID as ITEM_ID2_1_0_, item1_.ID as ID1_2_1_, item1_.NAME as NAME2_2_1_ from CATEGORY_TIMES items0_ inner join ITEM item1_ on items0_.ITEM_ID=item1_.ID where items0_.CATEGORY_ID=?
表结构
category:
item:
category_times:
单向多对多-关键代码
1.加上属性。 get、set方法略 private Set<Category> categorys = new HashSet<>(); 2.配置文件 <set name="categorys" sort="unsorted" table="CATEGORY_TIMES" inverse="true"> <key column="ITEM_ID" /> <many-to-many class="com.shuoeasy.test.Category" column="CATEGORY_ID" unique="false" /> </set>
Item.hbm.xml:
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <!-- Generated 2016-6-25 14:50:51 by Hibernate Tools 3.4.0.CR1 --> <hibernate-mapping default-access="field"> <class name="com.shuoeasy.test.Item" table="ITEM"> <id name="id" type="int"> <column name="ID" /> <generator class="native" /> </id> <property generated="never" lazy="false" name="name" type="java.lang.String"> <column name="NAME" /> </property> <set name="categorys" sort="unsorted" table="CATEGORY_TIMES" inverse="true"> <key column="ITEM_ID" /> <many-to-many class="com.shuoeasy.test.Category" column="CATEGORY_ID" unique="false" /> </set> </class> </hibernate-mapping>
