mybatis学习日记-连表查询-多对一

按照结果集嵌套查询

dao层：

package com.fu.dao;

import com.fu.pojo.Student;


import java.util.List;

public interface StudentMapper {

    //查询所有的学生信息以及其老师的信息
    List<Student> getStudentList();


}

package com.fu.dao;

public interface TeacherMapper {
}

pojo层：

package com.fu.pojo;

import org.apache.ibatis.type.Alias;

@Alias("student")
public class Student {
    private int id;
    private String name;
    private Teacher teacher;

    public Student(int id, String name, Teacher teacher) {
        this.id = id;
        this.name = name;
        this.teacher = teacher;
    }

    public Student() {
    }

    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;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", teacher=" + teacher +
                '}';
    }
}

package com.fu.pojo;

import org.apache.ibatis.type.Alias;

@Alias("teacher")
public class Teacher {
    private int id;
    private String name;

    public Teacher(int id, String name) {
        this.id = id;
        this.name = name;
    }

    public Teacher() {
    }

    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;
    }

    @Override
    public String toString() {
        return "Teacher{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}

dao层对应的student的xml：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.fu.dao.StudentMapper">


    <!--    方式一：按照结果嵌套处理-->
    <resultMap id="StudentTeacher" type="student">
        <result column="sid" property="id"/>
        <result column="sname" property="name"/>

        <!--       association：pojo中为对象，其中property对应的是实体类的字段，此处为学生表中的teacher，
                   javaType对应的是实体类的中属性的类型，比如在：private Teacher teacher;的类型就为Teacher

                   collection:pojo为集合，在一对多的时候使用
        -->
        <association property="teacher" javaType="teacher">
            <result column="tid" property="id"/>
            <result column="tname" property="name"/>
        </association>

    </resultMap>

    <select id="getStudentList" resultMap="StudentTeacher">
        SELECT student.`id` AS sid,student.`name` AS sname,student.`tid`AS stid,teacher.`id` AS tid,teacher.`name` AS tname
        FROM student,teacher
        WHERE student.`tid`=teacher.`id`
    </select>





</mapper>

测试类：

package com.fu.dao;

import com.fu.pojo.Student;
import com.fu.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;


import java.util.List;

public class StudentMapperTest {

    @Test
    public void getStudentListTest(){
        //获取sqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);

        List<Student> studentList = mapper.getStudentList();
        for (Student student : studentList) {
            System.out.println(student);
        }
        sqlSession.close();
    }
}

测试结果：