Mybatis结果集映射一对多简单入门教程 Mybatis结果集映射一对多简单入

Mybatis 一对多简单入门易懂
搭建数据库环境
student 表

DROP TABLE IF EXISTS `student_2`; CREATE TABLE `student_2`(`id` int(10) NOT NULL,`name` varchar(30) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,`tid` int(10) NULL DEFAULT NULL,PRIMARY KEY (`id`) USING BTREE,INDEX `fktid`(`tid`) USING BTREE,CONSTRAINT `fktid` FOREIGN KEY (`tid`) REFERENCES `teacher` (`id`) ON DELETE RESTRICT ON UPDATE RESTRICT) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic; INSERT INTO `student_2` VALUES (1, '小明', 1); INSERT INTO `student_2` VALUES (2, '邱ss', 2); INSERT INTO `student_2` VALUES (3, '邱大哥', 3); INSERT INTO `student_2` VALUES (4, '杨大哥', 1); INSERT INTO `student_2` VALUES (5, '杨ss', 2);

teacher

DROP TABLE IF EXISTS `teacher`; CREATE TABLE `teacher`(`id` int(10) NOT NULL AUTO_INCREMENT,`name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,PRIMARY KEY (`id`) USING BTREE) ENGINE = InnoDB AUTO_INCREMENT = 4 CHARACTER SET = latin1 COLLATE = latin1_swedish_ci ROW_FORMAT = Dynamic; -- ------------------------------ Records of teacher-- ----------------------------INSERT INTO `teacher` VALUES (1, '小王老师'); INSERT INTO `teacher` VALUES (2, '小李老师'); INSERT INTO `teacher` VALUES (3, '小黑老师');

idea 搭建maven 项目（mybatis-demo）
项目结构

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导入依赖

mysqlmysql-connector-java5.1.48org.projectlomboklombok1.18.20org.mybatismybatis3.5.6junitjunit4.11test

mysql 配置文件

jdbc.driver=com.mysql.jdbc.Driverjdbc.url=jdbc:mysql://localhost:3306/ssm-study?useSSL=falsejdbc.username=rootjdbc.password=123456

创建pojo 类
学生

/** * @Author: crush * @Date: 2021-06-17 18:23 * version 1.0 */public class Student {/*** 学生id*/private Integer id; /*** xueshneg xingming*/private String name; /*** 老师id*/private Integer tid; }

老师

/** * @Author: crush * @Date: 2021-06-17 18:23 * version 1.0 */public class Teacher {/*** 老师id*/private Integer id; /*** 老师的姓名*/private String name; /*** 每个老师是不是有很多学生*/private List students; }

写一个mybatis 的工具类

/** * @author crush */public class MybatisUtil {private static SqlSessionFactory sqlSessionFactory; static {try {String resource="mybatis-config.xml"; InputStream inputStream= Resources.getResourceAsStream(resource); sqlSessionFactory=new SqlSessionFactoryBuilder().build(inputStream); } catch (IOException e) {e.printStackTrace(); }}public static SqlSession getSession(){return sqlSessionFactory.openSession(true); }}

写一个TeacherMapper

import com.crush.pojo.Teacher; import org.apache.ibatis.annotations.Param; import java.util.List; public interface TeacherMapper {// 获取老师List getTeacher(); //获取指定老师下的所有学生及老师的信息Teacher getTeacher2(@Param("tid") Integer id); //获取指定老师下的所有学生及老师的信息Teacher getTeacher3(@Param("tid") Integer id); }

写一个TeacherMapper.xml文件

select * from teacherselect s.id sid,s.name sname,t.name tname,t.id tid from student_2 s,teacher t where s.tid=t.id and t.id=#{tid}select * from teacher where id=#{tid}select* fromstudent_2 where tid=#{tid}

【Mybatis结果集映射一对多简单入门教程】mybatis-config.xml 文件

测试：

/** * @Author: crush * @Date: 2021-06-17 18:22 * version 1.0 */public class MyTest {@Testpublic void getTeacher(){SqlSession session = MybatisUtil.getSession(); TeacherMapper mapper = session.getMapper(TeacherMapper.class); List teacher = mapper.getTeacher(); System.out.println(teacher); session.close(); }@Testpublicvoid getTeacher2(){SqlSession session = MybatisUtil.getSession(); TeacherMapper mapper = session.getMapper(TeacherMapper.class); Teacher teacher2 = mapper.getTeacher2(1); System.out.println(teacher2); session.close(); }@Testpublicvoid getTeacher3(){SqlSession session = MybatisUtil.getSession(); TeacherMapper mapper = session.getMapper(TeacherMapper.class); Teacher teacher2 = mapper.getTeacher3(1); System.out.println(teacher2); session.close(); }}

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