hibernate中多对多映射配置详细解析

    本工程以项目与开发人员构成多对多的关系来展开，构建多对多的关系，具体实现代码如下所示：

1.hibernate.cfg.xml文件

<!DOCTYPE hibernate-configuration PUBLIC"-//Hibernate/Hibernate Configuration DTD 3.0//EN""http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"><hibernate-configuration>    <!-- 通常，一个session-factory节点代表一个数据库 --><session-factory><!-- 1.数据库连接配置 --><property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property><property name="hibernate.connection.url">jdbc:mysql:///hib-demo</property><property name="hibernate.connection.username">root</property><property name="hibernate.connection.password">123456</property><!--数据库方法配置，hibernate在运行的时候，会根据不同的方言生成符合当前数据库语法的sql  --><property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property><!-- 2.其他相关配置 -->   <!--2.1显示hibernate在运行的时候执行的sql语句  --><property name="hibernate.show_sql">true</property>   <!-- 2.2格式化sql <property name="hibernate.format_sql">true</property>--><!--    2.3自动建表  --><property name="hibernate.hbm2ddl.auto">update</property><!-- 3.加载所有映射 <mapping resource="cn/itcast/a_hello/Employee.hbm.xml"/>--></session-factory></hibernate-configuration>

2.Developer

package cn.itcast.c_many2many;import java.util.HashSet;import java.util.Set;//开发人员信息public class Developer {private Integer d_id;//开发人员编号private String d_name;//开发人员姓名//开发人员参与的多个项目private Set<Project> projects=new HashSet<Project>();public Integer getD_id() {return d_id;}public void setD_id(Integer d_id) {this.d_id = d_id;}public String getD_name() {return d_name;}public void setD_name(String d_name) {this.d_name = d_name;}public Set<Project> getProjects() {return projects;}public void setProjects(Set<Project> projects) {this.projects = projects;}}

3.Project

package cn.itcast.c_many2many;import java.util.HashSet;import java.util.Set;public class Project {private Integer prj_id;//项目编号private String prj_name;//项目名称//项目下的多个员工private Set<Developer> developers=new HashSet<Developer>();public Integer getPrj_id() {return prj_id;}public void setPrj_id(Integer prj_id) {this.prj_id = prj_id;}public String getPrj_name() {return prj_name;}public void setPrj_name(String prj_name) {this.prj_name = prj_name;}public Set<Developer> getDevelopers() {return developers;}public void setDevelopers(Set<Developer> developers) {this.developers = developers;}}

4.Developer.hbm.xml

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><!--   This mapping demonstrates content-based discrimination for the  table-per-hierarchy mapping strategy, using a formula  discriminator.--><!--映射文件：映射一个实体类对象，描述一个对象最终可以直接保存对象数据到数据库中  --><!-- package:要映射的对象所在的包（可选，如果不指定，此文件下所有的类都要指定全路径）     auto-import 默认为true，在写HQL的时候自动导入包名            如果指定为false，在写HQL的时候必须要写上类的全名--><hibernate-mapping package="cn.itcast.c_many2many"><class name="Developer" table="t_developer">    <id name="d_id">       <generator class="native"></generator>    </id>    <property name="d_name"></property>       <set name="projects" table="t_relation">       <key column="did"></key>       <many-to-many column="prjId" class="Project"></many-to-many>    </set>         </class></hibernate-mapping>

5.Project.hbm.xml

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><!--   This mapping demonstrates content-based discrimination for the  table-per-hierarchy mapping strategy, using a formula  discriminator.--><!--映射文件：映射一个实体类对象，描述一个对象最终可以直接保存对象数据到数据库中  --><!-- package:要映射的对象所在的包（可选，如果不指定，此文件下所有的类都要指定全路径）     auto-import 默认为true，在写HQL的时候自动导入包名            如果指定为false，在写HQL的时候必须要写上类的全名--><hibernate-mapping package="cn.itcast.c_many2many"><class name="Project" table="t_project">    <id name="prj_id">       <generator class="native"></generator>    </id>    <property name="prj_name"></property>         <!-- 多对多映射：         1.映射的集合属性:developers         2.集合属性：对应的中间表，t_relation         3.外键字段：prjid         4.外键字段：对应的中间表字段，did         5.集合属性元素的类型 -->    <set name="developers" table="t_relation">        <key column="prjId"></key>        <many-to-many column="did" class="Developer"></many-to-many>    </set>             </class></hibernate-mapping>

6.junit测试

package cn.itcast.c_many2many;import org.hibernate.SessionFactory;import org.hibernate.Transaction;import org.hibernate.cfg.Configuration;import org.hibernate.classic.Session;import org.junit.Test;public class App_save {private static SessionFactory sf;static{sf=new Configuration().configure().addClass(Project.class).addClass(Developer.class)  //测试的时候使用.buildSessionFactory();}//多对多数据的保存，只能通过一方维护另一方，不能重复维护！@Testpublic void Save() {Session session=sf.openSession();session.beginTransaction();    //创建项目对象Project prj_ds=new Project();prj_ds.setPrj_name("电商系统");Project prj_oa=new Project();prj_oa.setPrj_name("OA系统");//创建员工对象Developer dev_cj=new Developer();dev_cj.setD_name("刘德华");Developer dev_wc=new Developer();dev_wc.setD_name("高园园");Developer dev_lz=new Developer();dev_lz.setD_name("王明");//关系prj_ds.getDevelopers().add(dev_cj);prj_ds.getDevelopers().add(dev_wc);//电商系统 ：刘德华，高园园prj_oa.getDevelopers().add(dev_cj);prj_oa.getDevelopers().add(dev_lz);//OA系统：刘德华，王明//保存session.save(dev_cj);session.save(dev_wc);session.save(dev_lz);session.save(prj_ds);session.save(prj_oa);session.getTransaction().commit();session.close();//得到九条结果/*Hibernate: insert into t_developer (d_name) values (?)Hibernate: insert into t_developer (d_name) values (?)Hibernate: insert into t_developer (d_name) values (?)Hibernate: insert into t_project (prj_name) values (?)Hibernate: insert into t_project (prj_name) values (?)Hibernate: insert into t_relation (prjId, did) values (?, ?)Hibernate: insert into t_relation (prjId, did) values (?, ?)Hibernate: insert into t_relation (prjId, did) values (?, ?)Hibernate: insert into t_relation (prjId, did) values (?, ?)*/}@Testpublic void Save2() {Session session=sf.openSession();session.beginTransaction();session.getTransaction().commit();session.close();}}