简单记录一下在java的Mybatis-plus中用一个SQL语句查询一个嵌套的实体类(实体类中有List,List中还有List)
也就是KpCourseInfoClientDetailVO课程详情类中含有List courseChapterList章节列表,然后章节列表中含有List lessonList课时列表,通过一个SQL查询得到结果
KpCourseInfoClientDetailVO类
java
@Data
public class KpCourseInfoClientDetailVO extends BaseEntity {
/**
* 主键ID
*/
@ApiModelProperty(value = "主键ID",example = "1" , position = 1)
private Long id;
/**
* 图片
*/
@ApiModelProperty(value = "图片",example = "https://yq-0.obs.cn-east-3.myhuaweicloud.com/12351.bjzgh.org/image/20220824/1661320343049.png" , position = 5)
private String pic;
/**
* 名称
*/
@ApiModelProperty(value = "名称",example = "Java修仙手册" , position = 11)
private String title;
/**
* 课时数量
*/
@ApiModelProperty(value = "课时数量",example = "5" , position = 21)
private Integer lessons;
/**
* 最近在学人数
*/
@ApiModelProperty(value = "最近在学人数",example = "5" , position = 31)
private Integer clicks;
/**
* 总学时
*/
@ApiModelProperty(value = "总学时(秒)",example = "120" , position = 35)
private Integer duration;
/**
* 已学时长
*/
@ApiModelProperty(value = "已学时长(秒)",example = "60" , position = 37)
private Integer studyDuration;
/**
* 章节列表
*/
@ApiModelProperty(value = "章节列表", position = 71)
private List<KpCourseChapterClientVO> courseChapterList;
}
KpCourseChapterClientVO类
java
@Data
public class KpCourseChapterClientVO extends BaseEntity {
/**
* 主键ID
*/
@ApiModelProperty(value = "主键ID",example = "1" , position = 1)
private Long id;
/**
* 名称
*/
@ApiModelProperty(value = "名称",example = "优秀奖《老年人便秘护理健康宣教》" , position = 51)
private String title;
/**
* 课时列表
*/
@ApiModelProperty(value = "课时列表", position = 71)
private List<KpLessonClientListVO> lessonList;
}
KpLessonClientListVO类
java
@Data
public class KpLessonClientListVO extends BaseEntity {
/**
* 主键ID
*/
@ApiModelProperty(value = "主键ID",example = "1" , position = 1)
private Long id;
/**
* 名称
*/
@ApiModelProperty(value = "名称",example = "走进故宫------下雪天的故宫是什么样的" , position = 31)
private String title;
/**
* 视频时长,单位:秒
*/
@ApiModelProperty(value = "视频时长,单位:秒",example = "120" , position = 111)
private Double duration;
}
首先在Navicat中验证SQL的准确性
sql
#查看前端课程详情
SELECT
kci.id,
kci.pic,
kci.title,
kci.lessons,
kci.clicks,
kci.duration,
kcc.id chapterId,
kcc.title chapterName,
kl.id lessonId,
kl.title lessonName,
kl.duration lessonDuration
FROM
kp_course_info kci
LEFT JOIN kp_course_chapter kcc ON kcc.course_id = kci.id
LEFT JOIN kp_lesson kl ON kl.chapter_id = kcc.id
WHERE
kci.id = 11567
AND kci.data_status = 0
AND kcc.data_status = 0
AND kl.data_status = 0
AND kl.available_flag = 1
AND kl.review_status = 5
ORDER BY kcc.id DESC
得到下列结果,说明SQL没有问题
然后在KpCourseInfoMapper.xml中实现
xml
<resultMap id="getCourseInfoDetail" type="com.chengyun.beijing.forms.exam.domain.vo.KpCourseInfoClientDetailVO">
<id property="id" column="id"></id>
<result property="pic" column="pic"></result>
<result property="title" column="title"></result>
<result property="lessons" column="lessons"></result>
<result property="clicks" column="clicks"></result>
<result property="duration" column="duration"></result>
<collection property="courseChapterList" ofType="com.chengyun.beijing.forms.exam.domain.vo.KpCourseChapterClientVO" column="chapterId">
<result property="id" column="chapterId"></result>
<result property="title" column="chapterName"></result>
<association property="lessonList" javaType="java.util.List" resultMap="lessonMap"/>
</collection>
</resultMap>
<resultMap id="lessonMap" type="com.chengyun.beijing.forms.exam.domain.vo.KpLessonClientListVO">
<result property="id" column="lessonId"></result>
<result property="title" column="lessonName"></result>
<result property="duration" column="lessonDuration"></result>
</resultMap>
<select id="getCourseInfoDetail" resultMap="getCourseInfoDetail">
SELECT
kci.id,
kci.pic,
kci.title,
kci.lessons,
kci.clicks,
kci.duration,
kcc.id chapterId,
kcc.title chapterName,
kl.id lessonId,
kl.title lessonName,
kl.duration lessonDuration
FROM
kp_course_info kci
LEFT JOIN kp_course_chapter kcc ON kcc.course_id = kci.id
LEFT JOIN kp_lesson kl ON kl.chapter_id = kcc.id
${ew.customSqlSegment}
</select>
因为是在实体类中List嵌套List,所以外部的List直接用collection 标签来写,然后再给其内部嵌套的List标签写个resultMap 来对应参数,最后通过接口调用就能拿到想要的参数结构了