hibernate 关联表中有其他属性处理方法

àì夳堔傛蜴生んèń 2022-06-15 08:58 157阅读 0赞

这个示例是为了解决关联表中有其他属性时该怎么配置、及操作。e-r图如下：

![e-r图][e-r]

一、本例中有三个类，分别为AAA、BBB、RRR，三个类的配置代码如下：

import java.util.HashSet;
    import java.util.Set;
    
    import javax.persistence.*;
    
    @Entity
    @Table(name="a")
    public class AAA {
    	@Id
    	@Column(name="aid")
    	@GeneratedValue(strategy = GenerationType.IDENTITY)
        private Integer aid;
        private String aname;
        @OneToMany(mappedBy="aaa")
    	private Set<RRR> rS = new HashSet<>();
        
        public AAA(){
        }
        public AAA(String aname){
        	this.aname = aname;
        }
        public AAA(Integer aid ,String aname){
        	this.aid = aid;
        	this.aname = aname;
        }
    	public Integer getAid() {
    		return aid;
    	}
    	public void setAid(Integer aid) {
    		this.aid = aid;
    	}
    	public String getAname() {
    		return aname;
    	}
    	public void setAname(String aname) {
    		this.aname = aname;
    	}
        public Set<RRR> getrS() {
    		return rS;
    	}
    	public void setrS(Set<RRR> rS) {
    		this.rS = rS;
    	}
    	public String toString(){
        	return "<aid:"+aid+" aname:"+aname+">";
        }
    }

import java.util.HashSet;
    import java.util.Set;
    
    
    import javax.persistence.Column;
    import javax.persistence.Entity;
    import javax.persistence.GeneratedValue;
    import javax.persistence.GenerationType;
    import javax.persistence.Id;
    import javax.persistence.OneToMany;
    import javax.persistence.Table;
    
    
    @Entity
    @Table(name = "b")
    public class BBB {
    	@Id
    	@Column(name = "bid")
    	@GeneratedValue(strategy = GenerationType.IDENTITY)
    	private Integer bid;
    	private String bname;
    	@OneToMany(mappedBy = "bbb")
    	private Set<RRR> rS = new HashSet<>();
    
    
    	public BBB(){
        }
        public BBB(String bname){
        	this.bname = bname;
        }
        public BBB(Integer bid ,String bname){
        	this.bid = bid;
        	this.bname = bname;
        }
    	
    	public Integer getBid() {
    		return bid;
    	}
    
    
    	public void setBid(Integer bid) {
    		this.bid = bid;
    	}
    
    
    	public String getBname() {
    		return bname;
    	}
    
    
    	public void setBname(String bname) {
    		this.bname = bname;
    	}
    
    
    	public String toString() {
    		return "<bid:" + bid + " bname:" + bname + ">";
    	}
    }

import java.io.Serializable;
    
    import javax.persistence.Column;
    import javax.persistence.Embeddable;
    import javax.persistence.EmbeddedId;
    import javax.persistence.Entity;
    import javax.persistence.JoinColumn;
    import javax.persistence.ManyToOne;
    import javax.persistence.Table;
    
    
    @Entity
    @Table(name="r")
    public class RRR {
    	@EmbeddedId
    	private Id id = new Id();
    	
    	private String rname;
    	@ManyToOne
    	@JoinColumn(name="aid",insertable=false,updatable=false)
    	private AAA aaa;
    	@ManyToOne
    	@JoinColumn(name="bid",insertable=false,updatable=false)
    	private BBB bbb;
        
    	
    	public RRR(){
        }
        public RRR(String rname){
        	this.rname = rname;
        }
        public RRR(String rname,AAA aaa,BBB bbb){
        	this.rname = rname;
        	this.aaa = aaa;
        	this.bbb = bbb;
        }
        public RRR(String rname, Integer aid, Integer bid){
        	this.rname = rname;
        	this.id = new Id(aid,bid);
        }
        
    	public String getRname() {
    		return rname;
    	}
    
    	public void setRname(String rname) {
    		this.rname = rname;
    	}
    
    	public AAA getAAA() {
    		return aaa;
    	}
    
    	public void setAAA(AAA aaa) {
    		this.aaa = aaa;
    	}
    
    	public BBB getBBB() {
    		return bbb;
    	}
    
    	public void setBBB(BBB bbb) {
    		this.bbb = bbb;
    	}
    	public String toString(){
        	return "<a:"+aaa.toString()+" b:"+bbb.toString()+" rname:"+rname+">";
        }
    	@Embeddable
    	public static class Id implements Serializable{
    		@Column(name="aid")
    		protected Integer aid;
    		@Column(name="bid")
    		protected Integer bid;
    		
    		public Id(){}
    		public Id(Integer aid, Integer bid){
    			this.aid = aid;
    			this.bid = bid;
    		}
    		
    		public boolean equals(Object o){
    			if(o!=null && o instanceof Id){
    				Id that = (Id)o;
    				return (this.aid.equals(that.aid))&&(this.bid.equals(that.bid));
    			}
    			return false;
    		}
    		
    		public int hashCode(){
    			return this.aid.hashCode() + this.bid.hashCode();
    		}
    		public Integer getAid() {
    			return aid;
    		}
    		public Integer getBid() {
    			return bid;
    		}
    	}
    }

二、实例操作

1、由 已知a 得到和 a 相关联的所有b

private void findBfromA(){
    		Integer aid = 1;
    		Session sess = HibernateUtil.currentSession();
    		Transaction tx = sess.beginTransaction();
    		Query query = sess.createQuery("from AAA where aid=:aid");
    		query.setParameter("aid", aid);
    		AAA a = (AAA) query.list().get(0);
    		
    		Set<RRR> rS = a.getrS();
    		List bList = new ArrayList<>();
    		for(RRR r: rS){
    			bList.add(r.getBBB());
    		}
    		System.out.println(bList.toString());
    		tx.commit();
    		HibernateUtil.closeSession();
    	}

结果示例：

[<bid:7 bname:新增b>, <bid:1 bname:b1>, <bid:2 bname:b2>, <bid:3 bname:b3>, <bid:4 bname:b4>]

2、向 r表 添加新的关联

// 向r中增加新关联
    	private void addToR() {
    		// 错误的方式
    		// AAA a = new AAA(1,"a1");
    		// BBB b = new BBB(7,"新增b");
    		// RRR r = new RRR("新增r");
    		// Session sess = HibernateUtil.currentSession();
    		// Transaction tx = sess.beginTransaction();
    		// r.setAAA(a);
    		// r.setBBB(b);
    		// sess.save(r);
    		// tx.commit();
    		// HibernateUtil.closeSession();
    
    		// 错误的方式
    		// AAA a = new AAA(7,"新增7");
    		// BBB b = new BBB(1,"b1");
    		// RRR r = new RRR("新增r2",a,b);
    		// Session sess = HibernateUtil.currentSession();
    		// Transaction tx = sess.beginTransaction();
    		// sess.save(r);
    		// tx.commit();
    		// HibernateUtil.closeSession();
    
    		// 正确的方式
    		RRR r = new RRR("新增r", 1, 7); //必须实例化Id类，必须设置aid、bid值，否则报错。
    		Session sess = HibernateUtil.currentSession();
    		Transaction tx = sess.beginTransaction();
    		sess.save(r);
    		tx.commit();
    		HibernateUtil.closeSession();
    	}

3、删除r表中的一条记录，两种方式

private void deleteR(){
    		//可以
    		AAA a = new AAA(1, "a1");
    		BBB b = new BBB(2, "b2");
    		Session sess = HibernateUtil.currentSession();
    		Transaction tx = sess.beginTransaction();
    		Query query = sess.createQuery("from RRR where aaa=:aaa and bbb=:bbb");
    		query.setParameter("aaa", a);
    		query.setParameter("bbb", b);
    		RRR r = (RRR) query.list().get(0);
    		sess.delete(r);
    		tx.commit();
    		HibernateUtil.closeSession();
    		
    	   //可以
    //		RRR r = new RRR("新增r", 1, 7);
    //		Session sess = HibernateUtil.currentSession();
    //		Transaction tx = sess.beginTransaction();
    //		sess.delete(r);
    //		tx.commit();
    //		HibernateUtil.closeSession();
    	}

三、数据库文件

/*
    Navicat MySQL Data Transfer
    
    Source Server         : dang
    Source Server Version : 50712
    Source Host           : 127.0.0.1:3306
    Source Database       : hibernate
    
    Target Server Type    : MYSQL
    Target Server Version : 50712
    File Encoding         : 65001
    
    Date: 2017-05-29 17:34:15
    */
    
    SET FOREIGN_KEY_CHECKS=0;
    
    -- ----------------------------
    -- Table structure for a
    -- ----------------------------
    DROP TABLE IF EXISTS `a`;
    CREATE TABLE `a` (
      `aid` int(11) NOT NULL AUTO_INCREMENT,
      `aname` varchar(255) DEFAULT NULL,
      PRIMARY KEY (`aid`)
    ) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8;
    
    -- ----------------------------
    -- Records of a
    -- ----------------------------
    INSERT INTO `a` VALUES ('1', 'a1');
    INSERT INTO `a` VALUES ('2', 'a2');
    INSERT INTO `a` VALUES ('3', 'a3');
    INSERT INTO `a` VALUES ('4', 'a4');
    INSERT INTO `a` VALUES ('7', '新增a');
    
    -- ----------------------------
    -- Table structure for b
    -- ----------------------------
    DROP TABLE IF EXISTS `b`;
    CREATE TABLE `b` (
      `bid` int(11) NOT NULL AUTO_INCREMENT,
      `bname` varchar(255) DEFAULT NULL,
      PRIMARY KEY (`bid`)
    ) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8;
    
    -- ----------------------------
    -- Records of b
    -- ----------------------------
    INSERT INTO `b` VALUES ('1', 'b1');
    INSERT INTO `b` VALUES ('2', 'b2');
    INSERT INTO `b` VALUES ('3', 'b3');
    INSERT INTO `b` VALUES ('4', 'b4');
    INSERT INTO `b` VALUES ('7', '新增b');
    
    
    -- ----------------------------
    -- Table structure for r
    -- ----------------------------
    DROP TABLE IF EXISTS `r`;
    CREATE TABLE `r` (
      `aid` int(11) NOT NULL,
      `bid` int(11) NOT NULL,
      `rname` varchar(255) DEFAULT NULL,
      KEY `aid` (`aid`),
      KEY `bid` (`bid`),
      CONSTRAINT `aid` FOREIGN KEY (`aid`) REFERENCES `a` (`aid`) ON DELETE CASCADE ON UPDATE CASCADE,
      CONSTRAINT `bid` FOREIGN KEY (`bid`) REFERENCES `b` (`bid`) ON DELETE CASCADE ON UPDATE CASCADE
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
    
    -- ----------------------------
    -- Records of r
    -- ----------------------------
    INSERT INTO `r` VALUES ('1', '1', 'r1');
    INSERT INTO `r` VALUES ('1', '2', 'r2');
    INSERT INTO `r` VALUES ('1', '3', 'r3');
    INSERT INTO `r` VALUES ('1', '4', 'r4');
    INSERT INTO `r` VALUES ('2', '1', 'r5');
    INSERT INTO `r` VALUES ('2', '3', 'r6');
    INSERT INTO `r` VALUES ('2', '4', 'r7');
    INSERT INTO `r` VALUES ('3', '4', 'r7');
    INSERT INTO `r` VALUES ('1', '7', '新增r');

四、项目地址[点击打开链接][Link 1]

[e-r]: /images/20220615/0901acdf1b8844e8bbfa7083f0a17447.png
[Link 1]: https://github.com/efinedxq/HQL.git