Mybatis中联表查询（多对一）处理方式总结

1、创建表格环境，mySql中的数据表格如下：

CREATE TABLE `teacher` (
`id` INT(10) NOT NULL,
`name` VARCHAR(30) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8

INSERT INTO teacher(`id`, `name`) VALUES (1, '秦老师');

CREATE TABLE `student` (
`id` INT(10) NOT NULL,
`name` VARCHAR(30) DEFAULT NULL,
`tid` INT(10) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `fktid` (`tid`),
CONSTRAINT `fktid` FOREIGN KEY (`tid`) REFERENCES `teacher` (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('1', '小明', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('2', '小红', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('3', '小张', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('4', '小李', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('5', '小王', '1');

 

相关的表格对应关系如下：

 

 

 

多个学生对应一个老师

2、依据myBatis的官网搭建myBatis的测试环境

3、创建两个实体类

 

import lombok.Data;

@data

public class Student {
    private int id;
    private String name;
//    和老师关联起来
    private Teacher teacher;
}

 

@data
public class Teacher {
    private int id;
    private String name;
}

4、MyBatisUtils通用工具类

package com.liu.Utils;

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 java.io.IOException;
import java.io.InputStream;

public class MyBatisUtils {
//全局私有变量
    private static SqlSessionFactory sqlSessionFactory = null;
//加载数据库
    static {
        String resource = "mybatis-config.xml";
        InputStream inputStream = null;
        try {
            inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
//获取相应的sqlSession对象
    public static SqlSession getSqlSession(){
//        改为true后，则自动进行事务的提交
        SqlSession sqlSession = sqlSessionFactory.openSession(true);
        return sqlSession;
    }
}

5、mybatis-config.xml的配置（未设置日志）如下

 

<?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>
    <properties resource="db.properties"/>
    <settings>
        <setting name="mapUnderscoreToCamelCase" value="true"/>
    </settings>
    <typeAliases>
        <package name="com.liu.Pojo"/>
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="com/liu/Dao/StudentMapper.xml"/>
    </mappers>

</configuration>

 

 

 

6、创建StudentMapper接口

package com.liu.Dao;

import com.liu.Pojo.Student;

import java.util.List;

public interface StudentMapper {
    public List<Student> getStudent();
}

7、编辑StudentMapper.xml（重点）文件，进行结果集resultMap的映射

 

<?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.liu.Dao.StudentMapper">
    <select id="getStudent" resultMap="StudentTeacher">
        select s.id sid,s.name sname,t.name tname
        from mybatis.student s,mybatis.teacher t
        where s.tid=t.id;
    </select>
    <resultMap id="StudentTeacher" type="student">
        <id property="id" column="sid"/>
        <result property="name" column="sname"/>
        <association property="teacher" javaType="Teacher">
            <result property="name" column="tname"/>
        </association>
    </resultMap>
</mapper>

 

8、测试

import com.liu.Dao.StudentMapper;
import com.liu.Pojo.Student;
import com.liu.Utils.MyBatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class test02 {
    @Test
    public void test(){
        SqlSession sqlSession = MyBatisUtils.getSqlSession();
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        List<Student> student = mapper.getStudent();
        for (Student student1 : student) {
            System.out.println(student1);
        }
        sqlSession.close();
    }
}

9、测试结果