Mybatis的级联查询，分步查询，一对一，一对多和多对一

配置和代码目录

***util配置

***log4j配置 –可以打印入日志，也可以使用系统自带的STDOUT_LOGGING个人喜欢log4j

***mybatis-config.xml的配置

***jdbc.properties的大概配置​​​​​​​

1、studentMapper.xml

2、banjiMapper.xml

3、studentMapper.java、banjiMapper.java

4、banjiMapperTest.java

5、studentMapperTest.java

package com.xiaomin.util;

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 mybatisUtil {
    private static String path="mybatis-config.xml";
    private static SqlSessionFactory sqlSessionFactory;
    private static InputStream inputStream;;

    static {
        try {
            inputStream = Resources.getResourceAsStream(path);
            sqlSessionFactory=new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    public static SqlSession getSqlSession(){
        SqlSession sqlSession = sqlSessionFactory.openSession();
        return sqlSession;
    }
}

#????DEBUG????????console?file???????console?file?????????

log4j.rootLogger=DEBUG, console, file

#??????????

log4j.appender.console=org.apache.log4j.ConsoleAppender
log4j.appender.console.Target=System.out
log4j.appender.console.Threshold=DEBUG
log4j.appender.console.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=[%c]-%m%n

#?????????

log4j.appender.file=org.apache.log4j.RollingFileAppender
log4j.appender.file.File=./log/xiaomin.log
log4j.appender.file.MaxFileSize=100KB
log4j.appender.file.Threshold=DEBUG
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=[%p][%d{yy-MM-dd}][%c]-%m%n

#??????

log4j.logger.org.mybatis=DEBUG
log4j.logger.java.sql=DEBUG
log4j.logger.java.sql.Statement=DEBUG
log4j.logger.java.sql.ResultSet=DEBUG
log4j.logger.java.sql.preparedStatement=DEBUG

user=你自己的用户名
password=你自己的密码
driver=com.mysql.cj.jdbc.Driver    --8.x以上的connect就会有cj，旧版本没有cj
url=jdbc:mysql://localhost:3306/你自己的数据库

initsize = 5
maxsize = 50

1、studentMapper.xml

        select * from homework01_student st,homework01_banji ba
        where st.stu_banjiId=ba.banjiId and stu_num=#{stuNum}

        select * from homework01_student st,homework01_banji ba
        where st.stu_banjiId=ba.banjiId and stu_num=#{stuNum}

        select * from homework01_student

        select * from homework01_student s,homework01_banji b where banjiId=stu_banjiId

        select * from homework01_student where  stu_banjiId=#{bid}

2、banjiMapper.xml

        select * from homework01_banji where banjiId=#{banjiId}

        select * from homework01_banji b,homework01_student s where s.stu_banjiId=b.banjiId and banjiId=#{bid}

        select * from homework01_banji where banjiId=#{bid}

3、studentMapper.java、banjiMapper.java

package com.xiaomin.mapper;

import com.xiaomin.pojo.student;

import java.util.List;

public interface studentMapper {
    List getStudent();
    List getStudent2();
    student getStudentByTeacherId();
    List getAllStudentByNum(int stuNum);
    student getStudentByNum(int stuNum);

}

package com.xiaomin.mapper;

import com.xiaomin.pojo.banji;
import org.apache.ibatis.annotations.Param;

import java.util.List;

public interface banjiMapper {
    banji getBanji(int banjiId);
    List getBanji2(@Param("bid") int banjiId);
    List getBanji3(@Param("bid") int banjiId);
}

4、banjiMapperTest.java

package com.xiaomin.mapper;

import com.xiaomin.pojo.banji;
import com.xiaomin.util.mybatisUtil;
import org.apache.ibatis.session.SqlSession;
import org.apache.log4j.Logger;
import org.junit.jupiter.api.Test;

import java.util.List;

/**
 * @author 解你忧
 * @date 2022/03/25 23:14
 * @product_namae mybatis-software2
 * @product_namae IntelliJ IDEA
 */
public class banjiMapperTest {
    SqlSession sqlSession=mybatisUtil.getSqlSession();
    banjiMapper mapper=sqlSession.getMapper(banjiMapper.class);

    Logger logger = Logger.getLogger(studentMapperTest.class);
    @Test
    public void getBanji(){
        List banjiList = mapper.getBanji2(20010202);
        for (banji banji : banjiList) {
            System.out.println(banji);
        }
    }
    @Test
    public void getBanji2(){
        List banjiList = mapper.getBanji3(20010202);
        for (banji banji : banjiList) {
            System.out.println(banji);
        }
    }
}

5、studentMapperTest.java

package com.xiaomin.mapper;

import com.xiaomin.pojo.student;
import com.xiaomin.util.mybatisUtil;
import org.apache.ibatis.session.SqlSession;
import org.apache.log4j.Logger;
import org.junit.jupiter.api.Test;

import java.util.List;

/**
 * @author 解你忧
 * @date 2022/03/22/23:14
 */
public class studentMapperTest {
    SqlSession sqlSession= mybatisUtil.getSqlSession();
    studentMapper mapper = sqlSession.getMapper(studentMapper.class);

    Logger logger = Logger.getLogger(studentMapperTest.class);
    @Test
    public void getAllStudentByNum(){
        List studentAndBanjiInfo = mapper.getAllStudentByNum(2032002);
        for (student student : studentAndBanjiInfo) {
            System.out.println(student);
        }
        sqlSession.close();
    }
    @Test
    public void getStudentByNum(){
        student linmin = mapper.getStudentByNum(2032002);
        System.out.println(linmin);
        sqlSession.close();
    }
    @Test
    public void getStudent(){
        List studentList = mapper.getStudent();
        for (student student : studentList) {
            System.out.println(student);
        }
        sqlSession.close();
    }
    @Test
    public void getStudent2(){
        List studentList = mapper.getStudent2();
        for (student student : studentList) {
            System.out.println(student);
        }
        sqlSession.close();
    }
}

Original: https://www.cnblogs.com/jieniyou/p/16417727.html
Author: 解你忧
Title: Mybatis的级联查询，分步查询，一对一，一对多和多对一