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！
    @Test
    public 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 (?, ?)
  */
       
    }
   
    @Test
    public void Save2() {
       Session session=sf.openSession();
       session.beginTransaction();
     
    
        session.getTransaction().commit();
      session.close();
    
        
        
    }
}

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