先搭一个Mybatis连MySQL数据库的环境

Navicat新建teacher和student两张数据表：

CREATE TABLE `teacher`
(`id`   INT(10) NOT NULL,`name` VARCHAR(30) DEFAULT NULL,PRIMARY KEY (`id`)
) ENGINE = INNODBDEFAULT CHARSET = utf8;INSERT INTO teacher(`id`, `name`)
VALUES (1, '秦老师');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 = INNODBDEFAULT CHARSET = utf8;INSERT 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);

对应的student表：

对应的teacher表：

一对多的实现：

对应的实体类：Student.class:

@Data
public class Student {private Integer id;private String name;//一对多private Integer tid;//多对一
//    private Teacher teacher;
}

对应的实体类：Student.class

@Data
public class Teacher {
private Integer id;
private String name;
//一对多
private List students;
}
对应的Mapper接口：TeacherMapper.java

public interface TeacherMapper extends BaseMapper {//一对多（集合）public List<Teacher> manyToOne();
}

对应的mapper.xml文件：teacher.xml

<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.liang.mapper.TeacherMapper">
<!--    一对多的集合处理--><select id="manyToOne" resultMap="teacherMap">select s.id sid,s.name sname,s.tid sid,t.id tid,t.name tname from student s,teacher t;</select><resultMap id="teacherMap" type="com.liang.pojo.Teacher"><id property="id" column="tid"></id><result property="name" column="tname"></result>
<!--        参数说明-->
<!--        property：Teacher类中对应的属性student，javaType是实体类student对应的类型；ofType:用来指定映射到List或者集合中的 pojo类型，泛型中的约束类型--><collection property="students" javaType="List" ofType="com.liang.pojo.Student" resultMap="getStudent">
<!--            <id property="id" column="id"></id>-->
<!--            <result property="name" column="name"></result>-->
<!--            <result property="tid" column="tid"></result>--></collection></resultMap><resultMap id="getStudent" type="com.liang.pojo.Student"><id property="id" column="sid"></id><result property="name" column="sname"></result><result property="tid" column="sid"></result></resultMap>
</mapper>

测试类：

public class StudentMapperTest {@Resourceprivate StudentMapper studentMapper;@Resourceprivate TeacherMapper teacherMapper;@Testpublic void testOneToMany(){List<Teacher> teachers =teacherMapper.manyToOne();System.out.println("----------------------------");System.out.println("----------------------------");System.out.println("----------------------------");System.out.println(teachers.get(1));System.out.println("----------------------------");System.out.println("----------------------------");System.out.println("----------------------------");for (Teacher teacher : teachers) {System.out.println(teacher);}System.out.println("----------------------------");System.out.println("----------------------------");System.out.println("----------------------------");}
}

单元测试结果：