mapper.xml层，实体类一对多关系怎么写？

实体类层：

import lombok.Data;
import java.util.List;
/**
 * 教师对象 teacher
 */
@Data
public class Teacher {

    /** 教师id */
    private String id;
    /** 教师名称 */
    private String teacherName;
    /** 性别 */
    private String sex;
    /** 年龄 */
    private int age;
    /** 科目列表 */
    private List<Subject> subjectList;
}

import lombok.Data;
/**
 * 科目对象 subject
 */
@Data
public class Subject {

    /** 科目id */
    private String id;
    /** 科目名称 */
    private String subjectName;
    /** 科目教室 */
    private String classroom;
    /** 课程时间（分钟） */
    private String courseTime;
}

import lombok.Data;
/**
 * 教师关系科目 teacher_relation_subject
 */
@Data
public class TeacherRelationSubject {

    /** id */
    private String id;
    /** 教师ID */
    private String teacherId;
    /** 科目id */
    private String subjectId;

}

mapper.xml层

collection：表示关联查询的结果集;
property： 表示关联查询的结果集映射到实体类的那个属性中；
ofType： 指定关联查询的结果集映射的对象类型；
select : 表示关联的查询语句；
column: 表示关联的字段名称。

<?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.rckj.check.mapper.TeacherMapper">

    <resultMap type="Teacher" id="TeacherResult">
        <result property="id"    column="id"    />
        <result property="teacherName"    column="teacher_name"    />
        <result property="sex"    column="sex"    />
        <result property="age"    column="age"    />
        <collection property="subjectList" ofType="com.rckj.check.domain.Subject"
                    select="findSubjectById" column="id"/>
    </resultMap>
   
    <select id="findSubjectById" resultMap="SubjectResult">
        SELECT * FROM subject s
        LEFT JOIN teacher_relation_subject trs on s.id = trs.subject_id
        WHERE trs.teacher_id = #{id}
    </select>

    <resultMap type="com.rckj.check.domain.Subject" id="SubjectResult">
        <result property="id"    column="id"    />
        <result property="subjectName"    column="subject_name"    />
        <result property="classroom"    column="classroom"    />
        <result property="courseTime"    column="course_time"    />
    </resultMap>

    <sql id="selectTeacherVo">
        select id, teacher_name, sex, age from teacher
    </sql>

    <select id="selectTeacherList" parameterType="Teacher" resultMap="TeacherResult">
        <include refid="selectTeacherVo"/>
        <where>
            <if test="teacherName != null  and teacherName != ''">teacher_name like concat('%', #{teacherName}, '%')</if>
        </where>
    </select>

    <select id="selectTeacherById" parameterType="String" resultMap="TeacherResult">
        <include refid="selectTeacherVo"/>
        where id = #{id}
    </select>

    <insert id="insertTeacher" parameterType="Teacher">
        insert into teacher
        <trim prefix="(" suffix=")" suffixOverrides=",">
            <if test="id != null">id,</if>
            <if test="teacherName != null">teacher_name,</if>
            <if test="sex != null">sex,</if>
            <if test="age != null">age,</if>
         </trim>
        <trim prefix="values (" suffix=")" suffixOverrides=",">
            <if test="id != null">#{id},</if>
            <if test="teacherName != null">#{teacherName},</if>
            <if test="sex != null">#{sex},</if>
            <if test="age != null">#{age},</if>
         </trim>
    </insert>

    <update id="updateTeacher" parameterType="TPortfolioProject">
        update teacher
        <trim prefix="SET" suffixOverrides=",">
            <if test="teacherName != null">teacher_name = #{teacherName},</if>
            <if test="sex != null">sex = #{sex},</if>
            <if test="age != null">age = #{age},</if>
        </trim>
        where id = #{id}
    </update>

    <delete id="deleteTeacherById" parameterType="String">
        delete from teacher where id = #{id}
    </delete>

    <delete id="deleteTeacherIds" parameterType="String">
        delete from teacher where id in
        <foreach item="id" collection="array" open="(" separator="," close=")">
            #{id}
        </foreach>
    </delete>
</mapper>