時(shí)間：2017年07月11日星期二
說(shuō)明：本文部分內(nèi)容均來(lái)自慕課網(wǎng)。@慕課網(wǎng)：http://www.imooc.com
教學(xué)源碼：無(wú)
學(xué)習(xí)源碼：https://github.com/zccodere/s...

案例分析：企業(yè)項(xiàng)目開(kāi)發(fā)過(guò)程中

一個(gè)項(xiàng)目可由多個(gè)員工參與開(kāi)發(fā)
一個(gè)員工可同時(shí)參與開(kāi)發(fā)多個(gè)項(xiàng)目

示意圖

多對(duì)多關(guān)聯(lián)

多對(duì)多關(guān)聯(lián)關(guān)系也是常見(jiàn)的一種關(guān)聯(lián)關(guān)系，如項(xiàng)目和員工之間就是典型的多對(duì)多關(guān)系
多對(duì)多關(guān)聯(lián)關(guān)系一般采用中間表的形式來(lái)實(shí)現(xiàn)，即新增一張包含關(guān)聯(lián)雙方主鍵的關(guān)聯(lián)表
多對(duì)多關(guān)聯(lián)可以使用元素和元素進(jìn)行配置

創(chuàng)建一個(gè)maven項(xiàng)目，名為hibernatemtm，POM文件如下

    4.0.0

    com.myimooc
    hibernatemtm
    0.0.1-SNAPSHOT
    jar

    hibernatemtm
    http://maven.apache.org

    
        UTF-8
        UTF-8
    

    
        
        
            org.hibernate
            hibernate-core
            4.3.0.Final
        

        
        
            mysql
            mysql-connector-java
            5.1.38
        
        
        
            junit
            junit
            3.8.1
            test
        
    

    
        
            
                org.apache.maven.plugins
                maven-compiler-plugin
                
                    1.8
                    1.8
                
            
        
    
    

創(chuàng)建表

create table project
(
    proid int primary key,
    proname varchar(20) not null
);

create table employee
(
    empid int primary key,
    empname varchar(20)
);

create table proemp
(
    rproid int,
    rempid int
);

alter table proemp add constraint fk_rproid 
    foreign key (rproid) references project(proid);
alter table proemp add constraint fk_rempid
    foreign key (rempid) references employee(empid);    
    
 

代碼演示

1.編寫(xiě)Project類

package com.myimooc.hibernatemtm.entity;

import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;

/**
 * project 實(shí)體類
 * @author ZhangCheng on 2017-07-11
 *
 */
public class Project implements Serializable{
    
    private static final long serialVersionUID = 1L;

    private int proid;
    
    private String proname;
    
    // 添加一個(gè)員工的集合
    private Set employees = new HashSet();

    public Project() {
    }

    public Project(int proid, String proname) {
        this.proid = proid;
        this.proname = proname;
    }

    public Project(int proid, String proname, Set employees) {
        this.proid = proid;
        this.proname = proname;
        this.employees = employees;
    }

    @Override
    public String toString() {
        return "Project [proid=" + proid + ", proname=" + proname + ", employees=" + employees + "]";
    }

    public int getProid() {
        return proid;
    }

    public void setProid(int proid) {
        this.proid = proid;
    }

    public String getproname() {
        return proname;
    }

    public void setproname(String proname) {
        this.proname = proname;
    }

    public Set getEmployees() {
        return employees;
    }

    public void setEmployees(Set employees) {
        this.employees = employees;
    }
    
    
}

2.編寫(xiě)Employee類

package com.myimooc.hibernatemtm.entity;

import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;

/**
 * employee 實(shí)體類
 * @author ZhangCheng on 2017-07-11
 *
 */
public class Employee implements Serializable{
    
    private static final long serialVersionUID = 1L;

    private int empid;
    
    private String empname;
    
    // 添加一個(gè)項(xiàng)目的集合
    private Set projects = new HashSet();

    public Employee() {
    }

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

    public Employee(int empid, String empname, Set projects) {
        this.empid = empid;
        this.empname = empname;
        this.projects = projects;
    }

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

    public int getEmpid() {
        return empid;
    }

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

    public String getEmpname() {
        return empname;
    }

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

    public Set getProjects() {
        return projects;
    }

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

}

代碼演示

1.編寫(xiě)Project.hbm.xml文件

2.編寫(xiě)Employee.hbm.xml文件

3.編寫(xiě)hibernate.cfg.xml文件

    
        org.hibernate.dialect.MySQLDialect
        com.mysql.jdbc.Driver
        root
        root
        
            
        
        true
        update
        
        
         
        
        
    

代碼演示

1.編寫(xiě)HibernateUtil類

package com.myimooc.hibernatemtm.util;

/**
 * session會(huì)話工具類
 * @author ZhangCheng on 2017-07-11
 *
 */
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {
    
    private static SessionFactory sessionFactory;
    
    private static Session session;

    static {
        // 創(chuàng)建Configuration對(duì)象，讀取hibernate.cfg.xml文件，完成初始化
        Configuration config = new Configuration().configure();
        StandardServiceRegistryBuilder ssrb = new StandardServiceRegistryBuilder()
                .applySettings(config.getProperties());
        StandardServiceRegistry ssr=ssrb.build();
        sessionFactory=config.buildSessionFactory(ssr);
    }
    
    /**
     * 獲取SessionFactory
     * @return
     */
    public static SessionFactory getSessionFactory(){
        return sessionFactory;
    }
    
    /**
     * 獲取Session
     * @return
     */
    public static Session getSession(){
        session=sessionFactory.openSession();
        return session;
    }
    
    /**
     * 關(guān)閉Session
     * @param session
     */
    public static void closeSession(Session session){
        if(session!=null){
            session.close();
        }
    }
}

2.編寫(xiě)Test類

package com.myimooc.hibernatemtm.test;

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

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

/**
 * 多對(duì)多關(guān)聯(lián)關(guān)系的配置
 * 同時(shí)建立了Project和Employee之間的雙向多對(duì)多關(guān)聯(lián)關(guān)系
 * 關(guān)聯(lián)關(guān)系的維護(hù)交由Project方來(lái)處理，并且在保存Project對(duì)象時(shí)會(huì)一并保存Employee對(duì)象
 * @author ZhangCheng on 2017-07-11
 */
public class Test {
    public static void main(String[] args) {
        Project project1=new Project(1001,"項(xiàng)目一");
        Project project2=new Project(1002,"項(xiàng)目二");
        Employee employee1=new Employee(1,"慕女神");
        Employee employee2=new Employee(2,"imooc");
        
        //參加項(xiàng)目1的員工有慕女神和imooc
        project1.getEmployees().add(employee1);
        project1.getEmployees().add(employee2);
        // 參加項(xiàng)目2的員工有慕女神
        project2.getEmployees().add(employee1);
        
        Session session=HibernateUtil.getSession();
        Transaction tx=session.beginTransaction();
        session.save(project1);
        session.save(project2);
        tx.commit();
        HibernateUtil.closeSession(session);
    }
}

課程總結(jié)

實(shí)現(xiàn)多對(duì)多關(guān)聯(lián)關(guān)系
在數(shù)據(jù)庫(kù)底通過(guò)添加中間表來(lái)指定關(guān)聯(lián)關(guān)系
    在雙方的實(shí)體中添加一個(gè)保存對(duì)方的集合
    在雙方的映射文件中使用元素和元素進(jìn)行關(guān)聯(lián)關(guān)系的配置