多对多关联配置
Hibernate的多对多关联关系的重点就是它的配置和它的级联操作，今天就拿书籍表（t_hibernate_book）、书籍类别表（t_hibernate_category）和中间表（t_hibernate_book_category）为例
先上代码
这是我的book.hbm.xml文件,这里主要参数介绍set中的many-to-many，class就是它映射的另外一个实体类，详细都在代码中有注释
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.xy.four.entity.Book" table="t_hibernate_book">
<cache usage="read-only" region="com.zking.five.entity.Book"/>
<id name="bookId" type="java.lang.Integer" column="book_id">
<generator class="increment" />
</id>
<property name="bookName" type="java.lang.String"
column="book_name">
</property>
<property name="price" type="java.lang.Float"
column="price">
</property>
<!--
table:代表的是中间表
name:书籍类的关联属性
inverse:中间表交于对方维护
key:当前类对应的表列段在中间表（t_hibernate_book_category）中的外键bid
many-to-many
colmn：对应的是上面key查出来中间表(t_hibernate_book_category)的另一个字段(cid)，当作关联表的主键(category_id)进行查询
流程：以查询book_id=8圣墟这本书为例
1、通过建模反射自动生成Sql，可以拿到book_id=8的基本信息
2、book_id=8->bid=8去查询中间表t_hibernate_book_category,拿到了cid=8,9
3、cid=8,9->t_hibernate_book_catego中的category_id=8,9
4、拿到了当前Book实例对应的category的集合
5、最终书本的信息{book_id=8,book_name=圣墟,price=40}->{{book_id=8,book_name=圣墟,price=40,categorys=[{...},{...}]}}
-->
<set table="t_hibernate_book_category" name="categories" cascade="save-update" inverse="false">
<!-- one -->
<key column="bid"></key>
<!-- many -->
<many-to-many column="cid" class="com.xy.four.entity.Category"></many-to-many>
</set>
</class>
</hibernate-mapping>
书籍映射文件category.hbm.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.xy.four.entity.Category" table="t_hibernate_category">
<id name="categoryId" type="java.lang.Integer" column="category_id">
<generator class="increment" />
</id>
<property name="categoryName" type="java.lang.String"
column="category_name">
</property>
<set table="t_hibernate_book_category" name="books" cascade="save-update" inverse="true">
<key column="cid"></key>
<many-to-many column="bid" class="com.xy.four.entity.Book"></many-to-many>
</set>
</class>
</hibernate-mapping>
级联新增 inverse属性值的设置
参数inverse；
总共四种 (false 是控制方 ，true 是被控制方)，其中有两种正确，两种错误
1、book：false category:true ✓（将维护的责任交给book）
2、book：true category:false ✓（将维护的责任交给category）
3、book：true category:true ✗
4、book：false category:false ✗
意思就是如果维护方是book,我在book表中新增了一条数据，那么中间表也会增加一条相关的数据，如果category是维护方则反之,删除也是一个道理，
案例代码：
BookDao
package com.xy.four.dao;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.query.Query;
import com.xy.four.entity.Book;
import com.xy.four.entity.Category;
import com.xy.two.util.SessionFactoryUtils;
public class BookDao{
public Integer addBook(Book book) {
Session session = SessionFactoryUtils.openSession();
Transaction transaction = session.beginTransaction();
Integer bid = (Integer) session.save(book);
transaction.commit();
session.close();
return bid;
}
public Integer addCategory(Category category) {
Session session = SessionFactoryUtils.openSession();
Transaction transaction = session.beginTransaction();
Integer cid = (Integer) session.save(category);
transaction.commit();
session.close();
return cid;
}
public Category getCategory(Category category) {
Session session = SessionFactoryUtils.openSession();
Transaction transaction = session.beginTransaction();
Category c = session.get(Category.class, category.getCategoryId());
transaction.commit();
session.close();
return c;
}
public Book getBook(Book book) {
Session session = SessionFactoryUtils.openSession();
Transaction transaction = session.beginTransaction();
Book b = session.get(Book.class, book.getBookId());
if (b != null && new Integer(1).equals(book.getInitCategories())) {
Hibernate.initialize(b.getCategories());
}
transaction.commit();
session.close();
return b;
}
public void delBook(Book book) {
Session session = SessionFactoryUtils.openSession();
Transaction transaction = session.beginTransaction();
session.delete(book);
transaction.commit();
session.close();
}
public void delCategory(Category category) {
Session session = SessionFactoryUtils.openSession();
Transaction transaction = session.beginTransaction();
Category c = session.get(Category.class, category.getCategoryId());
if(c!=null) {
for (Book b : c.getBooks()) {
// 通过在被控方通过主控方来解除关联关系，最后被控方再做删除
b.getCategories().remove(c);
}
}
session.delete(c);
transaction.commit();
session.close();
}
}
测试案例BookDaoTest
package com.xy.four.dao;
import org.junit.Test;
import com.xy.four.entity.Book;
import com.xy.four.entity.Category;
public class BookDaoTest {
private BookDao bookDao = new BookDao();
@Test
public void testGetBook() {
Book book = new Book();
book.setBookId(4);
book.setInitCategories(1);
Book b = this.bookDao.getBook(book );
System.out.println(b.getBookName());
System.out.println(b.getCategories());
}
/**
* book.hbm.xml inverse=fasle
* category.hbm.xml inverse=true
* 数据添加正常
* 书籍表、桥接表各新增一条数据
*/
@Test
public void test1() {
Book book = new Book();
book.setBookName("斗气化马");
book.setPrice(10f);
Category category = new Category();
category.setCategoryId(5);
// 直接将category对象加入到新建的book中是错误的，因为此时的category是临时态的，hibernate是不会管理的
// book.getCategories().add(category);
Category c = this.bookDao.getCategory(category);
// c.getBooks().add(book);
book.getCategories().add(c);
this.bookDao.addBook(book);
}
/**
* book.hbm.xml inverse=true
* category.hbm.xml inverse=true
* 只增加书籍表数据
* 桥接表不加数据
* 原因：双方都没有去维护关系
*/
@Test
public void test2() {
Book book = new Book();
book.setBookName("看我穿云箭");
book.setPrice(10f);
Category category = new Category();
category.setCategoryId(3);
Category c = this.bookDao.getCategory(category);
book.getCategories().add(c);
this.bookDao.addBook(book);
// c.getBooks().add(book);
}
}
我们用JUnit测试了增加方法，当我们book为false，category为true是，中间表也增加了一条数据
