app开发者平台在数字化时代的重要性与发展趋势解析
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2023-01-07
Mybatis结果集映射一对多简单入门教程
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
导入依赖
mysql 配置文件
jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/ssm-study?useSSL=false
jdbc.username=root
jdbc.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
}
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
//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
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
select * from teacher
select 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 * from student_2 where tid=#{tid}
mybatis-config.xml 文件
"http://mybatis.org/dtd/mybatis-3-config.dtd">
测试:
/**
* @Author: crush
* @Date: 2021-06-17 18:22
* version 1.0
*/
public class MyTest {
@Test
public void getTeacher(){
SqlSession session = MybatisUtil.getSession();
TeacherMapper mapper = session.getMapper(TeacherMapper.class);
List
System.out.println(teacher);
session.close();
}
@Test
public void getTeacher2(){
SqlSession session = MybatisUtil.getSession();
TeacherMapper mapper = session.getMapper(TeacherMapper.class);
Teacher teacher2 = mapper.getTeacher2(1);
System.out.println(teacher2);
session.close();
}
@Test
public void 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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