Hibernate 注解（Annotations 四）多对多双向注解

注解（Annotation），也叫元数据。一种代码级别的说明。它是JDK1.5及以后版本引入的一个特性，与类、接口、枚举是在同一个层次。它可以声明在包、类、字段、方法、局部变量、方法参数等的前面，用来对这些元素进行说明，注释。

接下来讲解多对多双向注解：

我以用户和房子作为示例讲解。

第一步：准备实体类

House（房间表）

package cn.manytomany.entity;

import javax.persistence.*;
import java.util.HashSet;
import java.util.Set;

/**
 * Created by accp on 2017/2/10.
 */
@Entity
@Table(name = "House")
public class House {
    @Id
    @GeneratedValue
    private Integer id;
    @Column
    private String title;
    @Column
    private String description;
    @Column
    private Integer price;
    @Column
    private String pubdate;
    @Column
    private Integer floorage;
    @Column
    private String contact;
    @Column
    private Integer userid;
    @Column
    private Integer streetid;
    @Column
    private Integer typeid;

    /**
     * 将控制权交给主表
     */
    @ManyToMany(mappedBy = "houses")
    private Set<Users> userss=new HashSet<Users>();

    public Integer getId() {
        return id;
    }

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

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public Integer getPrice() {
        return price;
    }

    public void setPrice(Integer price) {
        this.price = price;
    }

    public String getPubdate() {
        return pubdate;
    }

    public void setPubdate(String pubdate) {
        this.pubdate = pubdate;
    }

    public Integer getFloorage() {
        return floorage;
    }

    public void setFloorage(Integer floorage) {
        this.floorage = floorage;
    }

    public String getContact() {
        return contact;
    }

    public void setContact(String contact) {
        this.contact = contact;
    }

    public Integer getUserid() {
        return userid;
    }

    public void setUserid(Integer userid) {
        this.userid = userid;
    }

    public Integer getStreetid() {
        return streetid;
    }

    public void setStreetid(Integer streetid) {
        this.streetid = streetid;
    }

    public Integer getTypeid() {
        return typeid;
    }

    public void setTypeid(Integer typeid) {
        this.typeid = typeid;
    }

    public Set<Users> getUserss() {
        return userss;
    }

    public void setUserss(Set<Users> userss) {
        this.userss = userss;
    }
}

User（用户表）:

package cn.manytomany.entity;

import javax.persistence.*;
import java.util.HashSet;
import java.util.Set;

/**
 * Created by accp on 2017/2/10.
 */
@Entity
@Table(name = "Users")
public class Users {
    @Id
    @GeneratedValue
    private Integer id;
    @Column
    private String name;
    @Column
    private String password;
    @Column
    private String telephone;
    @Column
    private String username;
    @Column
    private String isadmin;
    /**
     * 以房间表作为主导  设置级联
     * 只需要保存用户  即可保存房间
     */
    @ManyToMany(cascade = {CascadeType.ALL})
    @JoinTable(
            name = "RUHS",
            joinColumns =@JoinColumn(name = "RUID"),
            inverseJoinColumns = @JoinColumn(name = "RHID")
    )
    private Set<House> houses=new HashSet<House>();

    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 String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getTelephone() {
        return telephone;
    }

    public void setTelephone(String telephone) {
        this.telephone = telephone;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getIsadmin() {
        return isadmin;
    }

    public void setIsadmin(String isadmin) {
        this.isadmin = isadmin;
    }

    public Set<House> getHouses() {
        return houses;
    }

    public void setHouses(Set<House> houses) {
        this.houses = houses;
    }
}

第二步：在hibernate.cfg.xml文件中配置<mapping>节点

<mapping class="cn.manytomany.entity.House"/>
<mapping class="cn.manytomany.entity.Users"/>

第三步：书写测试类

package cn.manytomany.test;

import cn.manytomany.entity.House;
import cn.manytomany.entity.Users;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

/**
 * Created by accp on 2017/2/10.
 */
public class DemoTest {
    Configuration cfg;
    Session session;
    Transaction tx;
    @Before
    public void myBefore(){
        cfg=new Configuration().configure();
        SessionFactory factory = cfg.buildSessionFactory();
        session = factory.openSession();
        tx=session.beginTransaction();
    }
    @After
    public void myAfter(){
        tx.commit();
        session.close();
    }
    @Test
    public void  add(){

        Users users1=new Users();
        users1.setName("hiber1");
        users1.setPassword("");
        users1.setTelephone("");
        users1.setUsername("Jim");
        users1.setIsadmin("");

        Users users2=new Users();
        users2.setName("hiber2");
        users2.setPassword("");
        users2.setTelephone("");
        users2.setUsername("Jim2");
        users2.setIsadmin("");

        House house=new House();
        house.setTitle("元宵佳节房屋便宜");
        house.setDescription("经济实惠，元宵佳宿！");
        house.setPrice();
        house.setPubdate("2017-02-11");
        house.setFloorage();
        house.setContact("圆圆");
        house.setStreetid();
        house.setTypeid();

        House house2=new House();
        house2.setTitle("共度元宵");
        house2.setDescription("便宜喽，赶快下手！");
        house2.setPrice();
        house2.setPubdate("2017-01-10");
        house2.setFloorage();
        house2.setContact("佳佳");
        house2.setStreetid();
        house2.setTypeid();

       /*关联关系
       * 同一个房间对应不同的用户
       *
       * 同一个用户对应不同的房间
       * */
        users1.getHouses().add(house);
        users1.getHouses().add(house2);
        users2.getHouses().add(house2);

        session.save(users1);
        session.save(users2);
    }
}

在配置多对多时要选取那张表生成第三张表非常重要，在第三张表的外键也要搞清楚。