mybais-多对一查询

准备阶段(多个学生对应一个老师)

1.建表

2.编写实体类

package com.lv.pojo;

import lombok.Data;

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

package com.lv.pojo;

import lombok.Data;

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

3.编写Mapper接口

package com.lv.dao;

public interface StudentMapper {
}

package com.lv.dao;

import com.lv.pojo.Teacher;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;

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

4.编写Mapper.xml配置文件

<?xml version="1.0" encoding="UTF8" ?>

<?xml version="1.0" encoding="UTF8" ?>

5.在mybatis-config.xml中添加映射

6.编写测试文件进行测试

package com.lv.dao;

import com.lv.pojo.Teacher;
import com.lv.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

public class MyTest {
    @Test
    public void getTeacher(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
        Teacher teacher = mapper.getTeacher(1);
        System.out.println(teacher);
        sqlSession.close();
    }
}

7.测试结果

方式一:按查询嵌套处理(相当于SQL中的子查询)

1.在StudentMapper接口中编写方法

//查询所有的学生信息,以及对应的老师信息!
public List getStudent();

2.编写对应的Mapper.xml文件

3.测试

@Test
public void getStudent(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
    List studentList = mapper.getStudent();
    for (Student student : studentList) {
        System.out.println(student);
    }
    sqlSession.close();
}

方式二:按结果嵌套处理(相当于SQL中的连表查询)

1.在StudentMapper接口中编写方法

//查询所有的学生信息,以及对应的老师信息!
public List getStudent2();

2.编写对应的Mapper.xml文件

3.测试

@Test
public void getStudent2(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
    List studentList = mapper.getStudent2();
    for (Student student : studentList) {
        System.out.println(student);
    }
    sqlSession.close();
}

mybatis-study

mybais-多对一查询

相关

标签