mybatis实战教程(四)-实现关联数据的查询

一对一查询

场景描述

一张银行卡只能有一个用户持有，那么银行卡和用户之间的关系就是一对一的关系。

操作步骤

1.创建一个名为infoManage数据库，并创建用户表User、用户银行卡账号信息表Card。代码如下：

#创建infoManage数据库
create database infoMange default character set utf8 collate utf8_general_ci;
#切换数据库
use infoMange;
#创建用户表User
create table if not exists user(
    id int not null auto_increment primary key,
    username varchar(20) not null unique,
    mobile varchar(11) not null unique,
    gender varchar(6) not null default 'male',
    age int not null
);

#创建银行卡账号信息表Card
create table if not exists card(
    id int not null auto_increment primary key,
    cardNum varchar(20) not null unique,
    userId int not null,
    foreign key(userId) references user(id)
);

#插入用户信息
insert into 
user(username,mobile,gender,age) 
values
('张三','13888888888','male',18),
('李四','13888888889','male',19),
('小花','13888888887','female',18),
('小柳','13888888886','female',21);
#插入银行卡信息
insert into 
card(cardNum,userId)
values
(6227888825370110828,1),
(6227888825370110827,4),
(6227888825370110825,3),
(6227888825370110824,2),
(6227888825370110823,1),
(6227888825370110821,3);

2.创建用户表实体类User及银行卡表实体类Card,代码如下：

用户表实体类User

//用户表实体类User
package com.zhq.pojo

public class User {
    private int id;
    private String username;
    private String mobile;
    private String gender;
    private int age;
    
    public void setId(int id){
        this.id = id;
    }
    
    public int getId(){
        return id;
    }
    
    public void setUsername(String username){
        this.username = username;
    }
    
    public String getUsername(){
        return username;
    }
    
    public void setMobile(String mobile){
        this.mobile = mobile;
    }
    
    public String getMobile(){
        return mobile;
    }
    
    public void setGender(String gender){
        this.gender = gender;
    }
    
    public String getGender(){
        return gender;
    }
    
    public void setAge(int age){
        this.age = age;
    }
    
    public int getAge(){
        return age;
    }
}

银行卡信息表card实体类Card

package com.zhq.pojo

public class Card {
    private int id;
    private String cardNum;
    private User user;
    
    public void setId(int id){
        this.id = id;
    }
    
    public int getId(){
        return id;
    }
        
    public void setCardNum(String cardNum){
        this.cardNum = cardNum;
    }
    
    public String getCardNum(){
        return cardNum;
    }
    
    public void setUser(User user){
        this.user = user;
    }
    
    public User getUser(){
        return user;
    }
}

3.配置XML映射文件CardMapper.xml、UserMapper.xml。配置信息如下：

CardMapper.xml配置信息

<?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.zhq.dao.CardDao">
    <!--执行两次查询-->
    <resultMap type="card" id="cardBaseMap">
         <id property="id" column="id" jdbcType=INTEGER/>
         <result property="cardNum" column="cardNum" jdbcType=VARCHAR/>
         <association property="user" column="user_id" javaType="user" select="getUser"/>
    </resultMap>
    <!--分两步查询-->
    <select id="getUser" parameterType="int" resultType="user">
        select * from user where id = #{id};
    </select>
    <select id="selectById" parameterType="int" resultMap="cardBaseMap">
        select * from card where id = #{id};
    </select>
    <!--执行一次查询-->
    <resultMap type="card" id="cardJoinUserBaseMap">
         <id property="id" column="id" jdbcType=INTEGER/>
         <result property="cardNum" column="cardNum" jdbcType=VARCHAR/>
         <association property="user" javaType="user">
                <id property="id" column="cid" jdbcType=INTEGER/>
                <result property="username" column="username" jdbcType=VARCHAR/>
                <result property="mobile" column="mobile" jdbcType=VARCHAR/>
                <result property="gender" column="gender" jdbcType=VARCHAR/>
                <result property="age" column="age" jdbcType= INTEGER/>
         </association>
    </resultMap>
    <!---联合查询->
    <select id="selectByJoinUser" parameterType="int" resultType="cardJoinUserBaseMap">
        select *,u.id uid from user u,card c where c.id = #{id} and c.userId=user.id;
    </select>
    <select id="selectAll" resultType="card">
        select * from card;
    </select>
</mapper>

UserMapper.xml配置信息

<?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.zhq.dao.UserDao">
    <resultMap type="user" id="userBaseMap">
          <id property="id" column="id" jdbcType=INTEGER/>
            <result property="username" column="username" jdbcType=VARCHAR/>
            <result property="mobile" column="mobile" jdbcType=VARCHAR/>
            <result property="gender" column="gender" jdbcType=VARCHAR/>
            <result property="age" column="age" jdbcType= INTEGER/>
    </resultMap>
    <select id="selectById" parameterType="int" resultMap="userBaseMap">
        select * from user where id = #{id};
    </select>
    <select id="selectAll" resultType="user">
        select * from user;
    </select>
</mapper>

4.配置mybatis_config文件,注册CardMapper.xml、UserMapper.xml。配置信息如下：

<mapper resource="com/zhq/mapper/CardMapper.xml"/>
<mapper resource="com/zhq/mapper/UserMapper.xml"/>

5.在com.zhq.test包下新创建一个名为CardTest测试类，测试代码如下：

package com.zhq.test;

import java.io.IOException;
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 org.junit.Assert;
import org.junit.Before;
import org.junit.Test;

import com.zhq.dao.CardDao;
import com.zhq.pojo.Card;

public class CardTest {
    private static SqlSessionFactory sqlSessionFactory;
    private static Reader reader;


    @Before
    public void setUp() throws Exception {
        try {
            reader = Resources.getResourceAsReader("mybatis_config.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //测试嵌套查询
    @Test
    public void select() {
        SqlSession session = sqlSessionFactory.openSession();
        CardDao cardDao = session.getMapper(cardDao.class);
        Card card = cardDao.selectById(1);
        session.commit();
        System.out.println(card);
        session.close();
    }
    
    //测试联合查询
    @Test
    public void select() {
        SqlSession session = sqlSessionFactory.openSession();
        CardDao cardDao = session.getMapper(CardDao.class);
        Card card = cardDao.selectByJoinUser(1);
        session.commit();
        System.out.println(card);
        session.close();
    }
}

一对多查询

场景描述

一个用户可以持有多张银行卡，那么用户和银行卡之间的关系就是一对多的关系。

操作步骤

1.修改User类，在User类中增加一个List<Card> cards属性表示该用户持有的银行卡，代码如下：

//用户表实体类User
package com.zhq.pojo

public class User {
    private int id;
    private String username;
    private String mobile;
    private String gender;
    private int age;
    private List<Card> cards;
    
    public void setId(int id){
        this.id = id;
    }
    
    public int getId(){
        return id;
    }
    
    public void setUsername(String username){
        this.username = username;
    }
    
    public String getUsername(){
        return username;
    }
    
    public void setMobile(String mobile){
        this.mobile = mobile;
    }
    
    public String getMobile(){
        return mobile;
    }
    
    public void setGender(String gender){
        this.gender = gender;
    }
    
    public String getGender(){
        return gender;
    }
    
    public void setAge(int age){
        this.age = age;
    }
    
    public int getAge(){
        return age;
    }
    
    public void setCards(List<Card> cards){
        this.cards = cards;
    }
    
    public List<Card> getCards(){
        return cards;
    }
}

2.修改UserMapper.xml配置文件。如下所示：

<?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.zhq.dao.UserDao">
    <resultMap type="user" id="userBaseMap">
          <id property="id" column="id" jdbcType=INTEGER/>
            <result property="username" column="username" jdbcType=VARCHAR/>
            <result property="mobile" column="mobile" jdbcType=VARCHAR/>
            <result property="gender" column="gender" jdbcType=VARCHAR/>
            <result property="age" column="age" jdbcType= INTEGER/>
            <collection property="cards" ofType="card" column="id" select="getCards"></collection>
    </resultMap>
    
    <select id="getCards" parameterType="int" resultType="card">
        select * from card where userId = #{id};
    </select>
    
    <select id="selectById" parameterType="int" resultMap="userBaseMap">
        select * from user where id = #{id};
    </select>
    
    <select id="selectAll" resultType="user">
        select * from user;
    </select>
</mapper>

3.在com.zhq.test包下新创建一个名为UserTest测试类，测试代码如下：

package com.zhq.test;

import java.io.IOException;
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 org.junit.Assert;
import org.junit.Before;
import org.junit.Test;

import com.zhq.dao.UserDao;
import com.zhq.pojo.User;

public class UserTest {
    private static SqlSessionFactory sqlSessionFactory;
    private static Reader reader;


    @Before
    public void setUp() throws Exception {
        try {
            reader = Resources.getResourceAsReader("mybatis_config.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //测试嵌套查询
    @Test
    public void select() {
        SqlSession session = sqlSessionFactory.openSession();
        UserDao userDao = session.getMapper(UserDao.class);
        User user = userDao.selectById(1);
        session.commit();
        System.out.println(user);
        session.close();
    }
    
}

多对多的查询

多对多的查询其实就是两个一对多的查询