Hibernate的多对多映射

一、创建Java工程，新建Lib文件夹，加入Hibernate和数据库（如MySql、Oracle、SqlServer等）的Jar包，创建 hibernate.cfg.xml 文件，并配置，配置项如下：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
    
        <!-- 配置连接数据库的基本信息 -->
        <property name="connection.username">root</property>
        <property name="connection.password"></property>
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <!-- <property name="connection.url">jdbc:mysql:///mis</property> -->
        <property name="connection.url">
            <![CDATA[jdbc:mysql://localhost:3306/mis?useUnicode=true&characterEncoding=utf8]]>
        </property>


        <!-- 配置 hibernate 的基本信息 -->
        <!-- hibernate 所使用的数据库方言 -->
        <property name="dialect">org.hibernate.dialect.MySQL5Dialect</property>

        <!-- 执行操作时是否在控制台打印 SQL -->
        <property name="show_sql">true</property>

        <!-- 是否对 SQL 进行格式化 -->
        <property name="format_sql">true</property>

        <!-- 指定自动生成数据表的策略 -->
        <property name="hbm2ddl.auto">update</property>
        
        <!-- 设置 Hibernate 的事务隔离级别 2:读已提交的记录-->
        <property name="connection.isolation">2</property>
        
        <!-- 删除对象后, 使其 OID 置为 null -->
        <property name="use_identifier_rollback">true</property>
        
        <!-- 配置 C3P0 数据源 -->
        <property name="hibernate.c3p0.max_size">10</property>
        <property name="hibernate.c3p0.min_size">5</property>
        <property name="c3p0.acquire_increment">2</property>
        
        <property name="c3p0.idle_test_period">2000</property>
        <property name="c3p0.timeout">2000</property>
        
        <property name="c3p0.max_statements">10</property>
        
        <!-- 设定 JDBC 的 Statement 读取数据的时候每次从数据库中取出的记录条数 -->
        <property name="hibernate.jdbc.fetch_size">100</property>
        
        <!-- 设定对数据库进行批量删除，批量更新和批量插入的时候的批次大小 -->
        <property name="jdbc.batch_size">30</property>

        <!-- 指定关联的 .hbm.xml 文件 -->    
        <!--  
        <mapping resource="com/mcs/hibernate/entities/onetoone/foreign/Manager.hbm.xml" />
        <mapping resource="com/mcs/hibernate/entities/onetoone/foreign/Department.hbm.xml" />
          -->
        <!--   
        <mapping resource="com/mcs/hibernate/entities/onetoone/primary/Manager.hbm.xml" />
        <mapping resource="com/mcs/hibernate/entities/onetoone/primary/Department.hbm.xml" />
         -->
        <!-- 
        <mapping resource="com/mcs/hibernate/entities/manytomany/Category.hbm.xml" />
        <mapping resource="com/mcs/hibernate/entities/manytomany/Product.hbm.xml" />
         -->
        <!--  
        <mapping resource="com/mcs/hibernate/entities/subclass/Person.hbm.xml" />
         -->
        <!--  
        <mapping resource="com/mcs/hibernate/entities/joined/subclass/Person.hbm.xml" />
         -->
        
        <mapping resource="com/mcs/hibernate/entities/union/subclass/Person.hbm.xml" />
        

    </session-factory>

</hibernate-configuration>

二、建立多对多的映射

1、创建Java实体类

package com.mcs.hibernate.entities.manytomany;

import java.util.HashSet;
import java.util.Set;

public class Category {
    
    private Integer id;
    private String name;
    
    private Set<Product> products = new HashSet<>();

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Set<Product> getProducts() {
        return products;
    }

    public void setProducts(Set<Product> products) {
        this.products = products;
    }
    
    

}

package com.mcs.hibernate.entities.manytomany;

import java.util.HashSet;
import java.util.Set;

public class Product {
    
    private Integer id;
    private String name;
    
    private Set<Category> categories = new HashSet<>();
    
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Set<Category> getCategories() {
        return categories;
    }
    public void setCategories(Set<Category> categories) {
        this.categories = categories;
    }
    
    

}

2、根据实体类创建对应的 hbm.xml文件

<?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 2015-10-28 14:53:27 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping>
    <class name="com.mcs.hibernate.entities.manytomany.Category" table="CATEGORIES">
        <id name="id" type="java.lang.Integer">
            <column name="ID" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="NAME" />
        </property>
        
        <!-- table: 指定中间表 -->
        <set name="products" table="CATEGORIES_PRODUCTS" inverse="true">
            <key>
                <column name="CATEGORY_ID" />
            </key>
            <!-- 使用 many-to-many 指定多对多的关联关系. column 执行 Set 集合中的持久化类在中间表的外键列的名称  -->
            <many-to-many class="com.mcs.hibernate.entities.manytomany.Product" column="PRODUCT_ID"/>
        </set>
    </class>
</hibernate-mapping>

<?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 2015-10-28 14:53:27 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping>
    <class name="com.mcs.hibernate.entities.manytomany.Product" table="PRODUCTS">
        <id name="id" type="java.lang.Integer">
            <column name="ID" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="NAME" />
        </property>
        
        <!-- table: 指定中间表 -->
        <set name="categories" table="CATEGORIES_PRODUCTS">
            <key>
                <column name="PRODUCT_ID" />
            </key>
            <!-- 使用 many-to-many 指定多对多的关联关系. column 执行 Set 集合中的持久化类在中间表的外键列的名称  -->
            <many-to-many class="com.mcs.hibernate.entities.manytomany.Category" column="CATEGORY_ID"/>
        </set>
    </class>
</hibernate-mapping>

3、备注：

　　1、使用 many-to-many 指定多对多的关联关系.

　　　　table: 指定中间表

　　　　Key：当前持久化类在中间表的外键列的名称

　　　　column：执行 Set 集合中的持久化类在中间表的外键列的名称

　　2、为了不重复更新，在其中的一端设置 inverse="true"的属性

　　3、在查询时需要连接中间表