Mybatis-Plus或PageHelper多表分页查询总条数不对问题的解决方法
目录
- 前言
- 一、问题说明
- 1、引入依赖
- 2、Mybatis-Plus配置
- 3、创建mapper层
- 4、编写xxxMapper.xml文件
- 5、测试一(不传任何条件,只分页)
- 5.1、结果总结
- 5.2、结果分析
- 6、测试二(传两个表的条件)
- 6.1、测试结果
- 6.2、结果总结
- 6.3、结果分析
- 二、解决
- 1、没条件查询只分页
- 2、两个表都有条件
- 3、结果总结
- 4、结果分析
- 5、最终方案
- 5.1、坑
- 三、结束语
前言
项目老大说项目需要重构搜索功能,决定交给我这个比较闲的人! 嗯 ???
因为以前的项目数据不大,都不能说不大,是很少,所有搜索采用的是MySQL中的like模糊搜索操作的,他希望我改一下;
我第一时间想到了ES,但他说没必要用ES,等以后数据量大了再换,现在只是稍微多了一些数据,没必要
Ok!那我就用了MySQL自带的全文检索功能,因为本文主要说的还是Mybatis-Plus的问题,所以全文检索在下面只会提到怎么使用,以及一些问题
好像说了一大堆废话,回归正题!
项目以前分页搜索用的是PageHelper这个插件,但公司封装的3.0框架中已经封装了Mybatis-Plus,所以我采用了Mybatis-Plus的分页插件
一、问题说明
场景:
老师表是有4条数据,每个老师对应2个学生
使用的是两个表联查letf join
加Mybatis
的级联查询,一次性获取所有数据出现3个问题:
1、数据总条数以及页数不对
2、数据分页数量不对
3、数据混乱
已下是我有问题的代码:
1、引入依赖
版本选择尽量3.4+
<dependency> <groupId>com.baomidou</groupId> <artifactId>mybatis-plus-boot-starter</artifactId> <version>3.5.1</version> </dependency>
2、Mybatis-Plus配置
@Configuration public class MybatisPlusConfig { /** * 插件注册 * * @param paginationInnerInterceptor 分页插件 * @return MybatisPlus拦截器 */ @Bean public MybatisPlusInterceptor mybatisPlusInterceptor(PaginationInnerInterceptor paginationInnerInterceptor) { MybatisPlusInterceptor mp = new MybatisPlusInterceptor(); mp.addInnerInterceptor(paginationInnerInterceptor); return mp; } //分页插件 @Bean public PaginationInnerInterceptor paginationInnerInterceptor() { PaginationInnerInterceptor pii = new PaginationInnerInterceptor(); pii.setMaxLimit(20L); pii.setDbType(DbType.MYSQL); //当超过最大页数时不会报错 pii.setOverflow(true); return pii; } }
3、创建mapper层
创建了一个返回实体类
TeacherVO
,包括老师信息以及学生信息,以及一个传入的参数类TeacherRequestVo
@Data public class TeacherVO { /** * 跟学生表关联的字段 */ private String classs; private String tname; private String tsex; private Date tbirthday; private String prof; private String depart; private List<Student> student; }
@Data public class TeacherRequestVo { private String classs; private String tname; private String sname; }
public interface TeacherMapper extends BaseMapper<Teacher> { /** * 获取老师所带班级中的所有老师及学生信息 * @param page mybatisplus自带的page类 * @param teacherRequestVo 传入的参数 * @return */ Page<TeacherVO> getAll(Page<TeacherVO> page, TeacherRequestVo teacherRequestVo); }
4、编写xxxMapper.xml文件
<resultMap id="GetAllMap" type="com.qjj.demo.entity.vo.TeacherVO"> <!--@mbg.generated--> <!--@Table teacher--> <result column="classs" jdbcType="VARCHAR" property="classs"/> <result column="Tname" jdbcType="VARCHAR" property="tname"/> <result column="Tsex" jdbcType="VARCHAR" property="tsex"/> <result column="Tbirthday" jdbcType="TIMESTAMP" property="tbirthday"/> <result column="Prof" jdbcType="VARCHAR" property="prof"/> <result column="Depart" jdbcType="VARCHAR" property="depart"/> <collection property="student" ofType="com.qjj.demo.entity.Student" resultMap="com.qjj.consumer.mapper.StudentMapper.BaseResultMap"/> </resultMap> <select id="getAll" resultMap="GetAllMap"> select * from teacher t left join student s on t.classs = s.classs <where> <if test="param2.size != null"> and s.size <![CDATA[ <= ]]> #{param2.size} </if> <if test="param2.classs != null and param2.classs != ''"> and t.classs = #{param2.classs} </if> <if test="param2.sname != null and param2.sname != ''"> and s.Sname = #{param2.sname} </if> <if test="param2.tname != null and param2.tname != ''"> and t.Tname = #{param2.tname} </if> </where> </select>
5、测试一(不传任何条件,只分页)
测试结果应该是二条数据,总数是四条
@RestController @RequestMapping("/demo") public class DemoController { @Resource private TeacherMapper teacherMapper; @PostMapping("/test3") public Page<TeacherVO> getAll(TeacherRequestVo teacherRequestVo) { Page<TeacherVO> teacherVOPage = new Page<>(1, 2); return teacherMapper.getAll(teacherVOPage, teacherRequestVo); } }
{ "records": [ { "classs": "804", "tname": "李诚", "tsex": "男", "tbirthday": "1958-12-02 00:00:00", "prof": "副教授", "depart": "计算机系", "student": [ { "sno": "108", "sname": "丘东", "ssex": "男", "sbirthday": "1977-09-01 00:00:00", "classs": null }, { "sno": "105", "sname": "匡明", "ssex": "男", "sbirthday": "1975-10-02 00:00:00", "classs": null } ] } ], "total": 4, "size": 2, "current": 1, "orders": [], "optimizeCountSql": true, "searchCount": true, "countId": null, "maxLimit": null, "pages": 2 }
5.1、结果总结
1、总条数正确
2、页数正确
3、数据不正确,返回条数不正确,应该返回两条数据,但现在只返回了一条
5.2、结果分析
查看它最终指向的sql语句
找到在
SimpleExecutor
下的doQuery
方法。
总条数的sql语句为:
SELECT COUNT(*) AS total FROM teacher t
分页语句为:
select * from teacher t left join student s on t.classs = s.classs LIMIT 2
拿去数据库运行结果为:
至此可以看出它只是获取了同一个老师下两个不同的学生信息;
而不是我们想象的两个老师,分别对应多个学生;
但总条数和条数正确
6、测试二(传两个表的条件)
得到的结果应该是一个老师对应他下面的两个学生
总条数是1
总数是1
6.1、测试结果
{ "records": [ { "classs": "804", "tname": "李诚", "tsex": "男", "tbirthday": "1958-12-02 00:00:00", "prof": "副教授", "depart": "计算机系", "student": [ { "sno": "108", "sname": "丘东", "ssex": "男", "sbirthday": "1977-09-01 00:00:00", "classs": null, "size": 1 }, { "sno": "105", "sname": "匡明", "ssex": "男", "sbirthday": "1975-10-02 00:00:00", "classs": null, "size": 2 } ] } ], "total": 2, "size": 2, "current": 1, "orders": [], "optimizeCountSql": true, "searchCount": true, "countId": null, "maxLimit": null, "pages": 1 }
6.2、结果总结
总条数不对
页数虽然对,但是那是因为我们分页的数量是2,而学生表中正好是一个老师对应两个学生,所以才对,但只要当一个老师对应3个学生或者超过2的话,页数也就不会对了,这里就不给大家测试了,大家可以自行测试一下
数据虽然看起来对的,但是跟页数是一样的道理,其实是错的
6.3、结果分析
还是查看它最终执行的SQL语句:
发现执行查询总条数的SQL语句有问题
SELECT COUNT(*) AS total FROM teacher t LEFT JOIN student s ON t.classs = s.classs WHERE s.size <= 3 AND t.classs = '804'
二、解决
在上面的测试中发现两个问题
1、数据不对
2、条数和页数不对
1、没条件查询只分页
我们修改
xxxMapper.xml
中的resultMap
采用级联查询
<resultMap id="GetAllMap" type="com.qjj.demo.entity.vo.TeacherVO"> <!--@mbg.generated--> <!--@Table teacher--> <result column="classs" jdbcType="VARCHAR" property="classs"/> <result column="Tname" jdbcType="VARCHAR" property="tname"/> <result column="Tsex" jdbcType="VARCHAR" property="tsex"/> <result column="Tbirthday" jdbcType="TIMESTAMP" property="tbirthday"/> <result column="Prof" jdbcType="VARCHAR" property="prof"/> <result column="Depart" jdbcType="VARCHAR" property="depart"/> <collection property="student" ofType="com.qjj.demo.entity.Student1" column="classs" select="getStudent"/> </resultMap> <select id="getAll" resultMap="GetAllMap"> select t.* from teacher t left join student s on t.classs = s.classs <where> <if test="param2.size != null"> and s.size <![CDATA[ <= ]]> #{param2.size} </if> <if test="param2.classs != null and param2.classs != ''"> and t.classs = #{param2.classs} </if> <if test="param2.sname != null and param2.sname != ''"> and s.Sname = #{param2.sname} </if> <if test="param2.tname != null and param2.tname != ''"> and t.Tname = #{param2.tname} </if> </where> </select> <select id="getStudent" resultMap="com.qjj.demo.mapper.Student1Mapper.BaseResultMap"> select * from student where classs = #{classs} </select>
{ "records": [ { "classs": "804", "tname": "李诚", "tsex": "男", "tbirthday": "1958-12-02 00:00:00", "prof": "副教授", "depart": "计算机系", "student": [ { "sno": "108", "sname": "丘东", "ssex": "男", "sbirthday": "1977-09-01 00:00:00", "classs": null, "size": 1 }, { "sno": "105", "sname": "匡明", "ssex": "男", "sbirthday": "1975-10-02 00:00:00", "classs": null, "size": 2 } ] }, { "classs": "804", "tname": "李诚", "tsex": "男", "tbirthday": "1958-12-02 00:00:00", "prof": "副教授", "depart": "计算机系", "student": [ { "sno": "108", "sname": "丘东", "ssex": "男", "sbirthday": "1977-09-01 00:00:00", "classs": null, "size": 1 }, { "sno": "105", "sname": "匡明", "ssex": "男", "sbirthday": "1975-10-02 00:00:00", "classs": null, "size": 2 } ] } ], "total": 4, "size": 2, "current": 1, "orders": [], "optimizeCountSql": true, "searchCount": true, "countId": null, "maxLimit": null, "pages": 2 }
2、两个表都有条件
{ "records": [ { "classs": "804", "tname": "李诚", "tsex": "男", "tbirthday": "1958-12-02 00:00:00", "prof": "副教授", "depart": "计算机系", "student": [ { "sno": "108", "sname": "丘东", "ssex": "男", "sbirthday": "1977-09-01 00:00:00", "classs": null, "size": 1 }, { "sno": "105", "sname": "匡明", "ssex": "男", "sbirthday": "1975-10-02 00:00:00", "classs": null, "size": 2 } ] }, { "classs": "804", "tname": "李诚", "tsex": "男", "tbirthday": "1958-12-02 00:00:00", "prof": "副教授", "depart": "计算机系", "student": [ { "sno": "108", "sname": "丘东", "ssex": "男", "sbirthday": "1977-09-01 00:00:00", "classs": null, "size": 1 }, { "sno": "105", "sname": "匡明", "ssex": "男", "sbirthday": "1975-10-02 00:00:00", "classs": null, "size": 2 } ] } ], "total": 2, "size": 2, "current": 1, "orders": [], "optimizeCountSql": true, "searchCount": true, "countId": null, "maxLimit": null, "pages": 1 }
3、结果总结
无条件时
数量正确,数据重复,页数正确
两表都有条件时:
总数不对,数据重复,页数不正确
4、结果分析
查看最终sql语句
查询总条数的SQL语句:
SELECT COUNT(*) AS total FROM teacher t LEFT JOIN student s ON t.classs = s.classs WHERE s.size <= ? AND t.classs = ?
查询老师表的SQL语句:
select t.* from teacher t left join student s on t.classs = s.classs WHERE s.size <= 3 and t.classs = "804" LIMIT 2
去数据库执行发现查询老师表的sql语句查出两条相同结果
其实到这里很多人都知道怎么解决了,只要去除重复的数据,所有问题都可以解决,无论是用去重,还是GROUP BY
都可以实现,我下面采用GROUP BY
5、最终方案
加上
GROUP BY
进行去重,其他地方都没改动
<select id="getAll" resultMap="GetAllMap"> select t.classs, t.Tname, t.Tsex, t.Tbirthday, t.Prof, t.Depart from teacher t left join student s on t.classs = s.classs <where> <if test="param2.size != null"> and s.size <![CDATA[ <= ]]> #{param2.size} </if> <if test="param2.classs != null and param2.classs != ''"> and t.classs = #{param2.classs} </if> <if test="param2.sname != null and param2.sname != ''"> and s.Sname = #{param2.sname} </if> <if test="param2.tname != null and param2.tname != ''"> and t.Tname = #{param2.tname} </if> </where> GROUP BY t.classs </select>
5.1、坑
进行分组的字段必须是主键,不然会报错
这里就不给大家展示测试结果了,没必要了,大家可自行测试
到这里问题完美解决
三、结束语
本人写过的所有解决什么问题都是项目中花了超过1个多小时才解决的问题,希望这篇文章对同学们有所帮助,不喜勿喷,有任何问题都可以评论,最后送上我的两句座右铭:
任何人都不会在意你成功的过程,只在意你成功的结果,在你没有成功之前,切勿向别人强调过程;
请不要假装努力,结果不会陪你演戏;
到此这篇关于Mybatis-Plus或PageHelper多表分页查询总条数不对问题的解决方法的文章就介绍到这了,更多相关Mybatis-Plus多表分页查询总条数不对内容请搜索我们以前的文章或继续浏览下面的相关文章希望大家以后多多支持我们!