该文章主要为完成实训任务，详细实现过程及结果见【http://t.csdn.cn/ZVEZd】

一、创建数据库表

1.1 创建教师表

• 执行SQL语句，创建教师表t_teacher

CREATE TABLE `t_teacher` (
`t_id` int(11) NOT NULL AUTO_INCREMENT,
`t_name` varchar(20) DEFAULT NULL,
PRIMARY KEY (`t_id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8mb4;

• 执行SQL语句，插入3条记录

INSERT INTO `t_teacher` VALUES ('1', '刘晓云');
INSERT INTO `t_teacher` VALUES ('2', '郑同华');
INSERT INTO `t_teacher` VALUES ('3', '李明军');

• 查看教师表记录
  

1.2 创建班级表

• 执行SQL语句，创建班级表t_class

CREATE TABLE `t_class` (`c_id` int(11) NOT NULL AUTO_INCREMENT,`c_name` varchar(20) DEFAULT NULL,`teacher_id` int(11) DEFAULT NULL,
PRIMARY KEY (`c_id`),
KEY `fk_teacher_id` (`teacher_id`),
CONSTRAINT `fk_teacher_id` FOREIGN KEY (`teacher_id`) REFERENCES `t_teacher` (`t_id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8mb4;

• 执行SQL语句，插入3条记录

INSERT INTO `t_class` VALUES ('1', '2021软件1班', '3');
INSERT INTO `t_class` VALUES ('2', '2021软件2班', '2');
INSERT INTO `t_class` VALUES ('3', '2021软件3班', '1');

• 查看班级表记录
  

1.3 创建学生表

• 执行SQL语句，创建学生表t_student

CREATE TABLE `t_student` (`s_id` int(11) NOT NULL AUTO_INCREMENT,`s_name` varchar(30) DEFAULT NULL,`s_gender` varchar(10) DEFAULT NULL,`s_age` int(11) DEFAULT NULL,`class_id` int(11) DEFAULT NULL,PRIMARY KEY (`s_id`)
) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8mb4;

• 执行SQL语句，插入9条记录

INSERT INTO `t_student` VALUES ('1', '佟大为', '男', '20', '1');
INSERT INTO `t_student` VALUEs ('2', '李方玉', '女', '19', '1');
INSERT INTO `t_student` VALUES ('3', '郑大林', '男', '19', '2');
INSERT INTO `t_student` VALUES ('4', '温晓辉', '男', '18', '1');
INSERT INTO `t_student` VALUES ('5', '吴文静', '女', '19', '2');
INSERT INTO `t_student` VALUES ('6', '肖文艳', '女', '18', '3');
INSERT INTO `t_student` VALUES ('7', '杨文军', '男', '20', '3');
INSERT INTO `t_student` VALUES ('8', '唐雨涵', '女', '19', '2');
INSERT INTo `t_student` VALUES ('9', '金雨欣', '女', '20', '2');

• 查看学生表记录
  

二、创建于数据库表对应的实体类

2.1 创建教师实体类

• 在cn.kox.mybatis.bean包里创建Teacher类
  

package cn.kox.mybatis.bean;/* @ClassName: Teacher* @Author: Kox* @Data: 2023/4/12* @Sketch:*/
public class Teacher {private int id;private String name;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}@Overridepublic String toString() {return "Teacher{" +"id=" + id +", name='" + name + '\\'' +'}';}
}

2.2 创建学生实体类

• 在cn.kox.mybatis.bean包里创建Student类
  

package cn.kox.mybatis.bean;/* @ClassName: Student* @Author: Kox* @Data: 2023/4/12* @Sketch:*/
public class Student {private int id;private String name;private String gender;private int age;private Clazz clazz;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getGender() {return gender;}public void setGender(String gender) {this.gender = gender;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public Clazz getClazz() {return clazz;}public void setClazz(Clazz clazz) {this.clazz = clazz;}@Overridepublic String toString() {return "Student{" +"id=" + id +", name='" + name + '\\'' +", gender='" + gender + '\\'' +", age=" + age +", clazz=" + clazz.getName() +'}';}
}

2.3 创建班级实体类

• 在cn.kox.mybatis.bean包里创建Clazz类
  

package cn.kox.mybatis.bean;import java.util.List;/* @ClassName: Clazz* @Author: Kox* @Data: 2023/4/12* @Sketch:*/
public class Clazz {private int id;private String name;private Teacher teacher;private List<Student> students;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Teacher getTeacher() {return teacher;}public void setTeacher(Teacher teacher) {this.teacher = teacher;}public List<Student> getStudents() {return students;}public void setStudents(List<Student> students) {this.students = students;}@Overridepublic String toString() {return "Clazz{" +"id=" + id +", name='" + name + '\\'' +", teacher=" + teacher.getName() +", students=" + students +'}';}
}

三、创建班级映射器配置文件

• 在resources/mapper目录里创建班级映射器配置文件ClazzMapper.xml
  

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="cn.kox.mybatis.mapper.ClazzMapper"><!--按编号查询班级（带教师信息和学生信息），需要三表关联查询--><select id="findById" parameterType="int" resultMap="clazzMap1">SELECT * FROM t_classINNER JOIN t_teacher ON t_class.teacher_id = t_teacher.t_idINNER JOIN t_student ON t_class.c_id = t_student.class_idWHERE c_id = #{id};</select><!--定义班级结果映射--><resultMap id="clazzMap1" type="Clazz"><result property="id" column="c_id"/><result property="name" column="c_name"/><!--一对一关联：一个班级配一个老师--><association property="teacher" javaType="Teacher" column="teacher_id"><result property="id" column="t_id"/><result property="name" column="t_name"/></association><!--一对多关联：一个班级有多个学生--><collection property="students" ofType="Student"><result property="id" column="s_id"/><result property="name" column="s_name"/><result property="gender" column="s_gender"/><result property="age" column="s_age"/><association property="clazz" javaType="Clazz" column="class_id"><result property="name" column="c_name"/></association></collection></resultMap><!--#--><!--查询全部班级（带教师信息，不带学生信息），利用嵌套查询实现一对一关联--><select id="findAll" resultMap="clazzMap2">SELECT * FROM t_class;</select><!--定义班级结果映射--><resultMap id="clazzMap2" type="Clazz"><result property="id" column="c_id"/><result property="name" column="c_name"/><!--通过select属性定义子查询--><association property="teacher" javaType="Teacher" column="teacher_id" select="getTeacher"/></resultMap><!--按编号查询教师--><select id="getTeacher" resultType="Teacher">SELECT t_id id, t_name name FROM t_teacher WHERE t_id = #{id};</select>
</mapper>

四、修改MyBatis配置文件

• 在配置文件里配置班级、教师与学生实体类别名，以及班级映射器配置文件
  

五、创建班级映射接口

• 在cn.kox.mybatis.mapper包里创建ClazzMapper接口
  

package cn.kox.mybatis.mapper;import cn.kox.mybatis.bean.Clazz;import java.util.List;public interface ClazzMapper {Clazz findById(int id); // 按编号查询班级记录List<Clazz> findAll();   // 查询全部班级记录
}

六、创建班级映射器测试类

• 在test/java目录的cn.kox.mybatis.mapper包里创建TestClazzMapper类
  

package cn.kox.mybatis.mapper;import cn.kox.mybatis.bean.Clazz;
import cn.kox.mybatis.bean.Student;
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.After;
import org.junit.Before;
import org.junit.Test;import java.io.IOException;
import java.io.Reader;
import java.util.List;/* @ClassName: TestClazzMapper* @Author: Kox* @Data: 2023/4/12* @Sketch:*/
public class TestClazzMapper {private SqlSession sqlSession; // SQL会话private ClazzMapper clazzMapper; // 班级映射器@Beforepublic void init() {try {// 读取MyBatis配置文件Reader reader = Resources.getResourceAsReader("mybatis-config.xml");// 基于MyBatis配置文件构建SQL会话工厂SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(reader);// 利用SQL会话工厂获取SQL会话sqlSession = factory.openSession();// 利用SQL会话获取班级映射器对象clazzMapper = sqlSession.getMapper(ClazzMapper.class);// 提示用户SQL会话创建成功System.out.println("SQL会话创建成功~");} catch (IOException e) {e.printStackTrace();}}@Test // 按编号查询班级（带教师信息和学生信息）public void testFindById() {// 查询id为1的班级信息int id = 1;Clazz clazz = clazzMapper.findById(id);// 判断是否查询成功if (clazz != null) {// 打印班级信息System.out.println(clazz);// 打印班级学生信息System.out.println("班级编号为[" + id + "]的学生：");List<Student> students = clazz.getStudents();students.forEach(student -> System.out.println(student));} else {System.out.println("编号为[" + id + "]的班级不存在~");}}@Test // 查询全部班级信息public void testFindAll() {// 查询全部班级List<Clazz> clazzes = clazzMapper.findAll();// 输出全部班级clazzes.forEach(clazz -> System.out.println(clazz));}@Afterpublic void destroy() {// 关闭SQL会话sqlSession.close();// 提示用户SQL会话关闭System.out.println("SQL会话已经关闭~");}
}

6.1 测试按编号查询班级方法

• 运行测试方法testFindById()，查看结果
  

6.2 测试查询全部班级方法

七、课后作业

7.1 创建三张表：学生表、选课表、课程表

• 学生表(学号, 姓名, 性别, 年龄, 电话) - 学号是字符串类型
• 选课表(学号, 课程号, 成绩)
• 课程表(课程号, 课程名, 课时数) - 课程号是字符串类型

7.2 给三张表输入若干记录

7.3 查询任务

7.3.1 按学号查询学生选课及成绩

• 查询结果包含字段：学号、姓名、课程名、成绩

7.3.2 查询全部学生选课及成绩

• 查询结果包含字段：学号、姓名、课程名、成绩