练习mybatis多对一关系

• 多个学生，对应一个老师
• 对于学生这边而言，关联， 多个学生，关联一个老师【多对一】

• 对于老师而言，集合，一个老师有很多学生【一对多】
  
  SQL：

  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, 计算机老师); 
  
  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=utf8INSERT 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);

  测试环境搭建
  1.导入lombok
  2.新建实体类Teacher，Student

  @Data
  public class Student{
    private int id;
    private String name;
    //学生需要关联一个老师！
    private Teacher teacher;
  }

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

  3.建立Dao接口TeacherDao，StudentDao

  public interface TeacherDao{
    @Select("select * from teacher where id=#{tid}")
    Teacher getTeacher(@Param("tid") int id);
  }

  public interface StudentDao{
  
  
  }

  4.建立Mapper.xml文件
  在resources目录创建com.jialidun.dao包

  <!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  <mapper namespace="com.jialidun.dao.TeacherDao">
    
  </mapper>

  <!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  <mapper namespace="com.jialidun.dao.StudentDao">
    
  </mapper>

  5.在核心配置文件中绑定注册我们的Mapper接口或者文件！

  <mappers>
    <mapper resource="com/jialidun/dao/*.xml"/>
    <mapper class="com.jialidun.dao.*"/>
  </mappers>

  6.测试查询成功

  public class TestDemo{
    @Test
    public void test01(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        TeacherDap mapper = sqlSession.getBean(TeacherDao.class);
        Teacher teacher = mapper.getTeacher(1);
        System.out.println(teacher);
        sqlSession.close();
    }
  
  
  }