3.Mybatis之多对一联表查询

实体Student与Teacher之间是多对一关系，现有要求查询学生并联表查询学生的老师，学生与老师是是一对多的关系，所以在学生实体类种添加Teacher属性。 Student.class

package com.xzf.pojo; import lombok.AllArgsConstructor; import lombok.Data; import lombok.NoArgsConstructor; @Data @AllArgsConstructor @NoArgsConstructor public class Student { private int id; private String name; private Teacher teacher; }

Teacher.class

package com.xzf.pojo; import lombok.AllArgsConstructor; import lombok.Data; import lombok.NoArgsConstructor; @Data @AllArgsConstructor @NoArgsConstructor public class Teacher { private int id; private String name; }

StudentMapper.java

package com.xzf.dao; import com.xzf.pojo.Student; import java.util.List; public interface StudentMapper { List<Student> getStudent(); List<Student> getStudent2(); }

StudentMapper.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.xzf.dao.StudentMapper"> <!-- 一对多第一种写法--> <select id="getStudent" resultMap="StudentTeacher"> select * from student </select> <resultMap id="StudentTeacher" type="Student"> <result property="id" column="id"></result> <result property="name" column="name"></result> <association property="teacher" column="tid" javaType="Teacher" select="getTeacher" ></association> </resultMap> <select id="getTeacher" resultType="Teacher"> select * from teacher where id = #{tid} </select> <!-- ———————————————————————————————————————————————————————————————————— --> <!-- 一对多第二种写法--> <select id="getStudent2" resultMap="StudentTeacher2"> select s.id as sid, s.name as sname, t.id as tid, t.name as tname from student s, teacher t where s.tid = t.id </select> <resultMap id="StudentTeacher2" type="Student"> <result property="id" column="sid"></result> <result property="name" column="sname"></result> <association property="teacher" javaType="Teacher"> <result property="id" column="tid"></result> <result property="name" column="tname"></result> </association> </resultMap> </mapper>

测试类

import com.xzf.dao.StudentMapper; import com.xzf.dao.TeacherMapper; import com.xzf.pojo.Student; import com.xzf.pojo.Teacher; import com.xzf.utils.MybatisUtil; import org.apache.ibatis.session.SqlSession; import org.junit.Test; import java.util.List; public class UserMapperTest { SqlSession sqlSession = MybatisUtil.getSqlSession(); @Test public void test2(){ StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class); List<Student> students = studentMapper.getStudent(); System.out.println(students); } @Test public void test3(){ StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class); List<Student> students = studentMapper.getStudent2(); System.out.println(students); } }

查询结果