Java学习：使用MyBatis Plus的分页插件和QueryWrapper结合自定义mapper xml实现多表关联查询

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Java学习：使用MyBatis Plus的分页插件和QueryWrapper结合自定义mapper xml实现多表关联查询

2023-05-29 16:17| 来源: 网络整理| 查看: 265

Vo：

/** * 用来返回给前端展示列表的数据实体 */ @Data public class CourseVo implements Serializable { private static final long serialVersionUID = 1L; private String id; private String title; private String subjectParentTitle; private String subjectTitle; private String teacherName; private Integer lessonNum; private String price; private String cover; private Long buyCount; private Long viewCount; private String status; private String gmtCreate; } /** * 专门用来接受课程列表查询参数的实体 */ @Data public class CourseQueryVo implements Serializable { private static final long serialVersionUID = 1L; private String title; private String teacherId; private String subjectParentId; private String subjectId; }

Controller：

public R index( @ApiParam(value = "当前页码", required = true) @PathVariable Long page, @ApiParam(value = "每页记录数", required = true) @PathVariable Long limit, @ApiParam(value = "查询对象") CourseQueryVo courseQueryVo){ IPage pageModel = courseService.selectPage(page, limit, courseQueryVo); List records = pageModel.getRecords(); long total = pageModel.getTotal(); return R.ok().data("total", total).data("rows", records); }

Service：

IPage selectPage(Long page, Long limit, CourseQueryVo courseQueryVo); public IPage selectPage(Long page, Long limit, CourseQueryVo courseQueryVo) { QueryWrapper queryWrapper = new QueryWrapper(); queryWrapper.orderByDesc("c.gmt_create"); String title = courseQueryVo.getTitle(); String teacherId = courseQueryVo.getTeacherId(); String subjectParentId = courseQueryVo.getSubjectParentId(); String subjectId = courseQueryVo.getSubjectId(); if (!StringUtils.isEmpty(title)) { queryWrapper.like("c.title", title); } if (!StringUtils.isEmpty(teacherId) ) { queryWrapper.eq("c.teacher_id", teacherId); } if (!StringUtils.isEmpty(subjectParentId)) { queryWrapper.eq("c.subject_parent_id", subjectParentId); } if (!StringUtils.isEmpty(subjectId)) { queryWrapper.eq("c.subject_id", subjectId); } Page pageParam = new Page(page, limit); //放入分页参数和查询条件参数，mp会自动组装 List records = baseMapper.selectPageByCourseQueryVo(pageParam, queryWrapper); pageParam.setRecords(records); return pageParam; }

Mapper：

List selectPageByCourseQueryVo(//mp会自动组装分页参数 Page pageParam, //mp会自动组装queryWrapper： //@Param(Constants.WRAPPER) 和 xml文件中的 ${ew.customSqlSegment} 对应 @Param(Constants.WRAPPER) QueryWrapper queryWrapper);

Mapper.xml

DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> c.id, c.title, c.lesson_num AS lessonNum, CONVERT(c.price, DECIMAL(8,2)) AS price, c.cover, c.buy_count AS buyCount, c.view_count AS viewCount, c.status, c.gmt_create AS gmtCreate, t.name AS teacherName, s1.title AS subjectParentTitle, s2.title AS subjectTitle edu_course c LEFT JOIN edu_teacher t ON c.teacher_id = t.id LEFT JOIN edu_subject s1 ON c.subject_parent_id = s1.id LEFT JOIN edu_subject s2 ON c.subject_id = s2.id SELECT FROM ${ew.customSqlSegment}

重点：MybatisPlus会将查询参数构成的条件和分页的page及limit自动组装到Sql中以后进行多表联合查询时，可以使用以下方法来进行数据的查找与筛选自动组装需要搭配：

@Param(Constants.WRAPPER) 放置于Mapper层接口的查询参数前，详细见上面代码例子

${ew.customSqlSegment} 将此行代码放置于Mapper文件的语句中，MybatisPlus将会为我们自动将 @Param(Constants.WRAPPER) 注解后的查询参数自动组装到Sql中

转： https://blog.csdn.net/StartedatAOP/article/details/109645540

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Java学习：使用MyBatis Plus的分页插件和QueryWrapper结合自定义mapper xml实现多表关联查询

Java学习：使用MyBatis Plus的分页插件和QueryWrapper结合自定义mapper xml实现多表关联查询

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