8.Hibernate的多对多关联映射

1.创建如下数据库脚本

--1.1 项目表
create table PROJECT
(
  proid   NUMBER(6) not null,
  proname VARCHAR2(50)
)
;
--1.2 项目表主键
alter table PROJECT
  add constraint PK_PROJECT_PROID primary key (PROID);


--2.1 员工表
create table EMPLOYEE
(
  empid   NUMBER(6) not null,
  empname VARCHAR2(50)
)
;

--2.2 员工表主键
alter table EMPLOYEE
  add constraint PK_EMPLOYEE_EMPID primary key (EMPID);

--3.1中间表
create table PROEMP
(
  rproid NUMBER(6) not null,
  rempid NUMBER(6) not null
)
;
--3.2 中间表主外健
alter table PROEMP
  add constraint PK_PROEMP primary key (RPROID, REMPID);

alter table PROEMP
  add constraint FK_PROEMP_REMPID foreign key (REMPID)
  references EMPLOYEE (EMPID);

alter table PROEMP
  add constraint FK_PROEMP_RPROID foreign key (RPROID)
  references PROJECT (PROID);

2.创建javaweb项目Hibernate_Part4_C2

3. 在项目的src下创建hibernate.cfg.xml的主配置文件

<?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>
     <!-- 数据库就的url地址 -->
     <property name="connection.url">jdbc:oracle:thin:@127.0.0.1:1521:orcl</property>
     
     <property name="dialect"> org.hibernate.dialect.Oracle10gDialect</property>
     
     <!-- 数据库驱动 -->
     <property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
     
     <!-- 数据库用户名 -->
     <property name="connection.username">scott</property>
     
     <!-- 数据库密码 -->
     <property name="connection.password">tiger</property>
     
 
     <!-- 显示sql语句 -->
     <property name="show_sql">true</property>
     
     <!-- sql语句格式化 -->
     <property name="format_sql">true</property>
     
     <!-- 注册映射文件 -->
     <mapping resource="com/entity/Project.hbm.xml"/>
     <mapping resource="com/entity/Employee.hbm.xml"/>
  </session-factory>
  
</hibernate-configuration>

4.在项目的src下的com.entity包下创建Employee.java类

package com.entity;

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

public class Employee {
    private Integer empid;
    private String empname;
    private Set<Project> projects=new HashSet<Project>();
    
    public Employee() {
    }

    public Employee(Integer empid, String empname) {
        this.empid = empid;
        this.empname = empname;
    }
    

    public Employee(Integer empid, String empname, Set<Project> projects) {
        this.empid = empid;
        this.empname = empname;
        this.projects = projects;
    }

    public Integer getEmpid() {
        return empid;
    }

    public void setEmpid(Integer empid) {
        this.empid = empid;
    }

    public String getEmpname() {
        return empname;
    }

    public void setEmpname(String empname) {
        this.empname = empname;
    }

    public Set<Project> getProjects() {
        return projects;
    }

    public void setProjects(Set<Project> projects) {
        this.projects = projects;
    }

    @Override
    public String toString() {
        return "Employee [empid=" + empid + ", empname=" + empname
                + ", projects=" + projects + "]";
    }
    

}

5.在项目的src下的com.entity包下创建Employee.hbm.xml映射文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
<hibernate-mapping>
   <!-- 持久化类的映射文件 -->
   <class name="com.entity.Employee" table="EMPLOYEE">
      <!-- 主键映射 -->
      <id name="empid" type="java.lang.Integer" column="empid">
         <!-- 主键插入由应用程序负责生成 -->
         <generator class="assigned"/>
      </id>
      <!-- 普通字段映射 -->
      <!-- 员工名称称映射 -->
      <property name="empname" type="java.lang.String" column="EMPNAME"/>
      
      <!-- 多对多 中间表字段-->
     <set name="projects" table="PROEMP" inverse="true">
        <!-- 中间表和员工表关联的外键字段 -->
         <key column="REMPID"></key>
         
         <!-- 员工中的项目集合 -->
         <many-to-many class="com.entity.Project" column="RPROID"/>
      </set>
   </class>
</hibernate-mapping>

6.在项目的src下的com.entity包下创建Project.java类

package com.entity;

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

public class Project {
    private Integer proid;
    private String proname;
    private Set<Employee> employees=new HashSet<Employee>();
    
    
    public Project() {
    }
    public Project(Integer proid, String proname) {
        this.proid = proid;
        this.proname = proname;
    }
    
    public Project(Integer proid, String proname, Set<Employee> employees) {
        this.proid = proid;
        this.proname = proname;
        this.employees = employees;
    }
    public Integer getProid() {
        return proid;
    }
    public void setProid(Integer proid) {
        this.proid = proid;
    }
    public String getProname() {
        return proname;
    }
    public void setProname(String proname) {
        this.proname = proname;
    }
    
    public Set<Employee> getEmployees() {
        return employees;
    }
    public void setEmployees(Set<Employee> employees) {
        this.employees = employees;
    }
    @Override
    public String toString() {
        return "Project [employees=" + employees + ", proid=" + proid
                + ", proname=" + proname + "]";
    }
    
    

}

7.在项目的src下的com.entity包下创建Project.hbm.xml映射文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
<hibernate-mapping>
   <!-- 持久化类的映射文件 -->
   <class name="com.entity.Project" table="PROJECT">
     <!-- 主键映射 -->
      <id name="proid" type="java.lang.Integer" column="PROID">
         <!-- 主键插入由应用程序负责生成 -->
         <generator class="assigned"/>
      </id>
      <!-- 普通字段映射 -->
      <!-- 项目名称称映射 -->
      <property name="proname" type="java.lang.String" column="PRONAME"/>
      <set name="employees" table="PROEMP" cascade="save-update">
      <!-- 中间表和项目表关联的外键字段 -->
         <key column="RPROID"></key>
         <many-to-many class="com.entity.Employee" column="REMPID"/>
      </set>
   </class>
</hibernate-mapping>

8.在项目的src下的com.util包下创建HibernateUtil.java类

package com.util;

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {
    /*
     * 1.创建用线程管理session的对象 还要导入org.hibernate.Session资源
     */
    private static final ThreadLocal<Session> threadLoad = new ThreadLocal<Session>();

    /*
     * 2.定义读取配置文件的对象
     */
    private static Configuration configuration = null;

    /*
     * 3.定义SessionFacotry工厂对象
     */
    private static SessionFactory sessionFactory = null;

    /*
     * 4.读取配置文件
     */
    static {
        try {
            // 读取配置文件
            configuration = new Configuration().configure();

            // 创建session工厂对象
            sessionFactory = configuration.buildSessionFactory();
        } catch (HibernateException e) {
            System.out.println("创建sessionFactory工厂对象错误");
            e.printStackTrace();
        }
    }

    /**
     * 5.获取Session对象
     * @return session对象
     */
    public static Session getSession() {
        // 获取当前线程内对应的session对象，可以保证每个线程都有自己的session独享
        Session session = threadLoad.get();

        // 如果获取的session为null则新打开session
        if (session == null) {
            // 打开一个新的Session
            session = sessionFactory.openSession();

            // 将session对象保存到线程中
            threadLoad.set(session);
        }
        // 返回从线程中获取的session对象
        return session;
    }
    
    /**
     * 6.关闭session对象
     */
    public static void closeSession(){
        //获取当前线程内对应的session对象，可以保证每个线程对象都有自己的session对象
        Session session=threadLoad.get();
        
        //将线程中的session置空
        threadLoad.set(null);
        
        //如果session不为空，则关闭session
        if(session!=null){
            //关闭session
            session.close();
        }
        
        
    }

}

9.在项目的src下的com.dao包下创建ProEmpDao.java类

package com.dao;

import org.hibernate.Session;
import org.hibernate.Transaction;

import com.entity.Employee;
import com.entity.Project;
import com.util.HibernateUtil;

public class ProEmpDao {
    public static void main(String[] args) {
        //开启session
        Session session=HibernateUtil.getSession();
        //开启事务
        Transaction tx=session.beginTransaction();
        //创建多个员工
        Employee emp1=new Employee(1, "张三");
        Employee emp2=new Employee(2, "李四");
        
        //创建项目存在
        Project p1=new Project(1, "1号项目");
        Project p2=new Project(2, "2号项目");
        
        //多个人负责一个项目
        p1.getEmployees().add(emp1);
        p1.getEmployees().add(emp2);
        
        //一个项目多个人负责
        emp1.getProjects().add(p1);
        emp2.getProjects().add(p1);
        
        //一个人负责多个项目
        p2.getEmployees().add(emp1);
        
        //一个项目一个人负责
        emp1.getProjects().add(p2);
        
        //保存项目时级联保存人信息
        session.save(p1);
        session.save(p2);
        
        tx.commit();
        HibernateUtil.closeSession();
        
        
    }

}