MyBatis之多對多關聯查詢

阿新 • • 發佈：2018-12-31

多對多關聯

myBatis的多對多關聯，是通過兩個一對多間接實現的

-- 使用者表
CREATE TABLE `user2`(
    `id` INT PRIMARY KEY AUTO_INCREMENT,
    `user_name` VARCHAR(20),-- 使用者姓名
    `address` VARCHAR(60)-- 聯絡地址
) ENGINE INNODB CHARSET utf8;
INSERT INTO `user2` VALUES(1,'陳大','深圳市南山區');
INSERT INTO `user2` VALUES(2,'王二','深圳市福田區');
INSERT INTO `user2` VALUES(3,'張三','深圳市龍華新區');
INSERT INTO `user2` VALUES(4,'李四','深圳市龍崗區');


-- 卡表
CREATE TABLE `card2`(
    `id` INT PRIMARY KEY AUTO_INCREMENT,
    `card_no` VARCHAR(18),
    `remark` VARCHAR(100)
) ENGINE=INNODB CHARSET=utf8;
INSERT INTO `card2` VALUES(1,'420001','會員卡');
INSERT INTO `card2` VALUES(2,'420002','會員卡');
INSERT INTO `card2` VALUES(3,'420003','會員卡');
INSERT INTO `card2` VALUES(4,'420004','會員卡');


-- 使用者、卡的中間表
CREATE TABLE `card2_user2`(
    `id` INT PRIMARY KEY AUTO_INCREMENT,
    `user_id` INT,
    `card_id` INT,
    `remark` VARCHAR(100)
);
INSERT INTO `card2_user2` VALUES(1,1,1,'');
INSERT INTO `card2_user2` VALUES(2,1,2,'');
INSERT INTO `card2_user2` VALUES(3,2,1,'');
INSERT INTO `card2_user2` VALUES(4,2,2,'');
INSERT INTO `card2_user2` VALUES(5,3,1,'');
INSERT INTO `card2_user2` VALUES(6,4,2,'');

-- SELECT * FROM `user2`;
-- SELECT * FROM `card2`;
-- SELECT * FROM `card2_user2`;
SELECT t1.`id`,
t2.`id` `user_id`,t2.`user_name`,t2.`address`,
t3.`id` `card_id`,t3.`card_no`,t3.`remark` `card_info`,
t1.`remark` 
FROM `card2_user2` t1,`user2` t2,`card2` t3 
WHERE t1.`user_id`=t2.`id` AND t1.`card_id`=t3.`id`;

實體類：Card1

package com.chensan.m2m.entity;

import java.util.List;

public class Card1 {
	private int id;
	private String cardNo;
	private String remark;
	private List<User1> users;
	
	public String toString(){
		return "[ id = " + id + ", cardNo = " + cardNo 
			+ ", remark = " + remark + "]";
	}
	//...省略setter、getter方法
}

實體類：User1

package com.chensan.m2m.entity;

import java.util.List;

public class User1 {
	private int id;
	private String userName;
	private String address;
	private List<Card1> cards;
	
	public String toString(){
		return "[ id = " + id  + ", userName = " 
			+ userName + ", address = " + address + "]";
	}
	//...省略setter、getter方法
}

實體類Card1對映檔案

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.chensan.m2m.entity.Card1Mapper">
  <resultMap id="card1Map" type="com.chensan.m2m.entity.Card1">
    <id property="id" column="card_id"/>
    <result property="cardNo" column="card_no"/>
    <result property="remark" column="card_info"/>
  </resultMap>
  
  <resultMap id="cardUserMap" type="com.chensan.m2m.entity.Card1" extends="card1Map">
    <collection property="users" ofType="com.chensan.m2m.entity.User1">
  	  <id property="id" column="user_id"/>
  	  <result property="userName" column="user_name"/>
  	  <result property="address" column="address"/>
  	</collection>
  </resultMap>
  
  <select id="query" parameterType="int" resultMap="cardUserMap">
  	SELECT t1.`id`,
	t2.`id` `card_id`,t2.`card_no`,t2.`remark` `card_info`,
	t3.`id` `user_id`,t3.`user_name`,t3.`address`,
	t1.`remark` 
	FROM `card2_user2` t1,`card2` t2,`user2` t3 
	WHERE t1.`user_id`=t2.`id` AND t1.`card_id`=t3.`id` 
	AND t2.`id`=#{id}
  </select>
</mapper>

實體類User1對映檔案

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.chensan.m2m.entity.User1Mapper">
  <resultMap id="user1Map" type="com.chensan.m2m.entity.User1">
  	<id property="id" column="user_id"/>
  	<result property="userName" column="user_name"/>
  	<result property="address" column="address"/>
  </resultMap>
  
  <resultMap id="userCardMap" type="com.chensan.m2m.entity.User1" extends="user1Map">
    <collection property="cards" ofType="com.chensan.m2m.entity.Card1">
	  <id property="id" column="card_id"/>
	  <result property="cardNo" column="card_no"/>
	  <result property="remark" column="card_info"/>
  	</collection>
  </resultMap>
  
  <select id="query" parameterType="int" resultMap="userCardMap">
  	SELECT t1.`id`,
	t2.`id` `user_id`,t2.`user_name`,t2.`address`,
	t3.`id` `card_id`,t3.`card_no`,t3.`remark` `card_info`,
	t1.`remark` 
	FROM `card2_user2` t1,`user2` t2,`card2` t3 
	WHERE t1.`user_id`=t2.`id` AND t1.`card_id`=t3.`id` 
	AND t2.`id`=#{id}
  </select>
</mapper>

使用extends實體類的方法是為了保留和擴充套件實體的操作；

myBatis配置檔案

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">

<configuration>
  <!-- 和spring整合後 environments配置將廢除-->
  <environments default="development">
	<environment id="development">
	  <!-- 使用jdbc事務管理  或者JTA事務管理-->
	  <transactionManager type="JDBC" />
	  <!-- 資料庫連線池  第三方元件：c3p0-->
	  <dataSource type="POOLED">
		<property name="driver" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/mybatis01"/>
        <property name="username" value="root"/>
        <property name="password" value="123456"/>
	  </dataSource>
	</environment>
  </environments>

  <!-- 載入實體類的對映檔案 -->
  <mappers>
    <mapper resource="com/chensan/m2m/mapper/User1Mapper.xml"/>
    <mapper resource="com/chensan/m2m/mapper/Card1Mapper.xml"/>
  </mappers>
</configuration>

測試類

package com.chensan.m2m.test;

import java.io.Reader;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import com.chensan.m2m.entity.Card1;
import com.chensan.m2m.entity.User1;

public class TestM2M {
	private static SqlSessionFactory sqlSessionFactory;
    private static Reader resource;
    
    //建立會話工廠
    static{
        try{
        	resource = Resources.getResourceAsReader("myBatisConfig.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(resource);
        }catch(Exception e){
            e.printStackTrace();
        }
    }
    
    public static SqlSessionFactory getSession(){
        return sqlSessionFactory;
    }
    
    //多對多：查詢使用者對應卡（會員卡）
    public void getUserCard(){
    	SqlSession sqlSession = sqlSessionFactory.openSession();
    	User1 user = sqlSession.selectOne("com.chensan.m2m.entity.User1Mapper.query", 1);
    	System.out.println(user);
    	for(Card1 card : user.getCards()){
    		System.out.println(
				"[ " + 
				"userId = " + user.getId() + ", " + 
				"userName = " + user.getUserName() + ", " + 
				"address = " + user.getAddress() + ", " + 
				"cardId = " + card.getId() + ", " + 
				"cardNo = " + card.getCardNo() + ", " + 
				"remark = " + card.getRemark() + 
				" ]"
			);
    	}
    	
    	sqlSession.close();
    }
    
  //多對多：查詢卡（會員卡）對應使用者
    public void getCardUser(){
    	SqlSession sqlSession = sqlSessionFactory.openSession();
    	Card1 card = sqlSession.selectOne("com.chensan.m2m.entity.Card1Mapper.query", 1);
    	System.out.println(card);
    	for(User1 user : card.getUsers()){
    		System.out.println(
				"[ " + 
				"cardId = " + card.getId() + ", " + 
				"cardNo = " + card.getCardNo() + ", " + 
				"remark = " + card.getRemark() + ", " + 
				"userId = " + user.getId() + ", " + 
				"userName = " + user.getUserName() + ", " + 
				"address = " + user.getAddress() + 
				" ]"
			);
    	}
    	
    	sqlSession.close();
    }
    
    public static void main(String[] args) {
    	TestM2M testMyBatisManyToMany = new TestM2M();
    	testMyBatisManyToMany.getUserCard();
    	testMyBatisManyToMany.getCardUser();
    }
}

結果如下：

[ id = 1, userName = 陳大, address = 深圳市南山區]
[ userId = 1, userName = 陳大, address = 深圳市南山區, cardId = 1, cardNo = 420001, remark = 會員卡 ]
[ userId = 1, userName = 陳大, address = 深圳市南山區, cardId = 2, cardNo = 420002, remark = 會員卡 ]
[ id = 1, cardNo = 420001, remark = 會員卡]
[ cardId = 1, cardNo = 420001, remark = 會員卡, userId = 1, userName = 陳大, address = 深圳市南山區 ]
[ cardId = 1, cardNo = 420001, remark = 會員卡, userId = 2, userName = 王二, address = 深圳市福田區 ]

請給同名列取別名

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