mybatis实现一对多的关系

这个需求就是一个对象里有多个类对象，比如有章节和小节，一个章节有多个小节，我们可以定义一个章节类，章节类里有一个小节类的集合，当前端循环遍历章节的同时可以在每个章节里遍历显示小节。

1.ChapterVo 章节类

package com.stu.eduservice.entity.chapter;

import lombok.Data;

import java.util.ArrayList;
import java.util.List;

@Data
public class ChapterVo {
    private String id;
    private String title;

    //小节
    private List<VideoVo> children = new ArrayList<>();
}

2.VideoVo小节类

package com.stu.eduservice.entity.chapter;

import lombok.Data;

@Data
public class VideoVo {
    private String id;
    private String title;
}

3.mapper接口

package com.stu.eduservice.mapper;

import com.stu.eduservice.entity.EduChapter;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.stu.eduservice.entity.chapter.ChapterVo;
import org.apache.ibatis.annotations.Mapper;

import java.util.List;

/**
 * <p>
 * 课程 Mapper 接口
 * </p>
 *
 * @author stu
 * @since 2021-05-29
 */

public interface EduChapterMapper extends BaseMapper<EduChapter> {
    List<ChapterVo> getChapterVideoByCourseId(String courseId);
}

4.mapper.xml

• resultmap里的column要和sql里的列名一致（如果有别名要和别名一致）
• property要和类里的属性名一致，jdbcType要和数据库里字段定义的类型一致
• collection里的property要和实体类里的集合属性名称一致，ofType是类的包名加上类名路径

<?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.stu.eduservice.mapper.EduChapterMapper">
    <resultMap id="BaseResultMap" type="com.stu.eduservice.entity.chapter.ChapterVo" >
        <id column="chapter_id" property="id" jdbcType="VARCHAR" />
        <result column="chapter_title" property="title" jdbcType="VARCHAR" />
        <collection property="children" ofType="com.stu.eduservice.entity.chapter.VideoVo">
            <id column="video_id" property="id" jdbcType="VARCHAR" />
            <result column="video_title" property="title" jdbcType="VARCHAR" />
        </collection>
    </resultMap>
    <select id="getChapterVideoByCourseId" parameterType="java.lang.String" resultMap="BaseResultMap">
        SELECT
            ec.id AS chapter_id,
            ec.title AS chapter_title,
            ev.id AS video_id,
            ev.title AS video_title
        FROM
            edu_chapter ec
            LEFT JOIN edu_video ev ON ev.chapter_id = ec.id
        WHERE
            ec.course_id = #{courseId}
    </select>
</mapper>

5.前端遍历

<!-- 章节 -->
<ul class="chanpterList">
    <li
        v-for="chapter in chapterVideoList"
        :key="chapter.id">
        <p>
            {{ chapter.title }}
        </p>

        <!-- 视频 -->
        <ul class="chanpterList videoList">
            <li
                v-for="video in chapter.children"
                :key="video.id">
                <p>{{ video.title }}
                </p>
            </li>
        </ul>
    </li>
</ul>

效果截图