PageHelper 分页无效的坑。。。

1.问题

阿里巴巴Java开发手册:

1.1.PageHelper先开启分页,后对list数据操作

@Override
public PageInfo<HdQueryVo> getRecordsByView(int pageNo, int pageSize) {
    PageHelper.startPage(pageNo,pageSize);
    List<HdQueryVo> hdQueryVosByView = actionMapper.getActionByView();

    List<HdQueryVo> hdQueryVos = new ArrayList<>();

    for (HdQueryVo hdQueryVo : hdQueryVosByView) {
        HdQueryVo hdQueryVoSingle = new HdQueryVo();
        hdQueryVoSingle.setHdId(hdQueryVo.getHdId());
        hdQueryVoSingle.setHdType(hdQueryVo.getHdType());
        hdQueryVoSingle.setHdTitle(hdQueryVo.getHdTitle());
        hdQueryVoSingle.setHdStartDate(hdQueryVo.getHdStartDate());
        hdQueryVoSingle.setHdEndDate(hdQueryVo.getHdEndDate());
        hdQueryVoSingle.setHdStatus(hdQueryVo.getHdStatus());
        hdQueryVoSingle.setHdImage(hdQueryVo.getHdImage());
        hdQueryVoSingle.setHdNumber(hdQueryVo.getHdNumber());
        hdQueryVoSingle.setGmtCreate(hdQueryVo.getGmtCreate());
        hdQueryVoSingle.setGmtModified(hdQueryVo.getGmtModified());
        hdQueryVoSingle.setUserId(hdQueryVo.getUserId());
        if (hdQueryVo.getHdType().equals(0)) {
            hdQueryVoSingle.setHdJoinUsers(onlineWorksMapper.getOnlineJoinUsers(hdQueryVo.getHdId()));
        } else {
            hdQueryVoSingle.setHdJoinUsers(offlineUsersMapper.getOfflineJoinUsers(hdQueryVo.getHdId()));
        }
        hdQueryVos.add(hdQueryVoSingle);
    }
    PageInfo<HdQueryVo> pageViewInfo = new PageInfo<>(hdQueryVos);

    return pageViewInfo;
}

可以分页,但是数据量错误,total始终等于每页数据量,即pageSize

1.2.先对list数据进行操作,后开启分页

@Override
public PageInfo<HdQueryVo> getRecordsByView(int pageNo, int pageSize) {
    
    List<HdQueryVo> hdQueryVosByView = actionMapper.getActionByView();

    List<HdQueryVo> hdQueryVos = new ArrayList<>();

    for (HdQueryVo hdQueryVo : hdQueryVosByView) {
        HdQueryVo hdQueryVoSingle = new HdQueryVo();
        hdQueryVoSingle.setHdId(hdQueryVo.getHdId());
        hdQueryVoSingle.setHdType(hdQueryVo.getHdType());
        hdQueryVoSingle.setHdTitle(hdQueryVo.getHdTitle());
        hdQueryVoSingle.setHdStartDate(hdQueryVo.getHdStartDate());
        hdQueryVoSingle.setHdEndDate(hdQueryVo.getHdEndDate());
        hdQueryVoSingle.setHdStatus(hdQueryVo.getHdStatus());
        hdQueryVoSingle.setHdImage(hdQueryVo.getHdImage());
        hdQueryVoSingle.setHdNumber(hdQueryVo.getHdNumber());
        hdQueryVoSingle.setGmtCreate(hdQueryVo.getGmtCreate());
        hdQueryVoSingle.setGmtModified(hdQueryVo.getGmtModified());
        hdQueryVoSingle.setUserId(hdQueryVo.getUserId());
        if (hdQueryVo.getHdType().equals(0)) {
            hdQueryVoSingle.setHdJoinUsers(onlineWorksMapper.getOnlineJoinUsers(hdQueryVo.getHdId()));
        } else {
            hdQueryVoSingle.setHdJoinUsers(offlineUsersMapper.getOfflineJoinUsers(hdQueryVo.getHdId()));
        }
        hdQueryVos.add(hdQueryVoSingle);
    }
    PageHelper.startPage(pageNo,pageSize);
    PageInfo<HdQueryVo> pageViewInfo = new PageInfo<>(hdQueryVos);

    return pageViewInfo;
}

数据可以查询出来,总数total也正确,但是分页功能失效。(这份阿里 Java 开发手册可以关注公众号Java核心技术,回复:手册)

2.原因

PageHelper中startPage开启分页方法只对后面的sql查询起作用

1.1 错误原因是提前开启分页后,对list操作,即PageInfo pageViewInfo = new PageInfo<>(hdQueryVos);

/**
* 包装Page对象
*
* @param list
*/
public PageInfo(List list) {
	this(list, 8);
}

只是把list转为PageInfo对象,不影响前面分页数据的操作

1.2 错误原因是先对list操作后,开启翻页后没有sql语句

即sql语句没有参与分页查询

3.解决方案

直接对分页后的PageInfo对象中的数据进行操作

  • 对list集合操作,先取出PageInfo里的list集合数据,再对数据进行相关操作
  • 将操作完后的list集合再次存到PageInfo里,进行return

@Override
public PageInfo<HdQueryVo> getRecordsByView(int pageNo, int pageSize) {
    PageInfo<HdQueryVo> source = PageHelper.startPage(pageNo, pageSize).doSelectPageInfo(()->{
        actionMapper.getActionByView();
    });
    // 需要转换的对象
    PageInfo<HdQueryVo> target = new PageInfo<>();
    // 复制分页属性
    BeanUtils.copyProperties(source, target);
    // 对查询的list进行下一步操作,比如类型转换后
    List<HdQueryVo> collect = source.getList().stream().collect(Collectors.toList());
    List<HdQueryVo> hdQueryVos = new ArrayList<>();

    for (HdQueryVo hdQueryVo : collect) {
        HdQueryVo hdQueryVoSingle = new HdQueryVo();
        hdQueryVoSingle.setHdId(hdQueryVo.getHdId());
        hdQueryVoSingle.setHdType(hdQueryVo.getHdType());
        hdQueryVoSingle.setHdTitle(hdQueryVo.getHdTitle());
        hdQueryVoSingle.setHdStartDate(hdQueryVo.getHdStartDate());
        hdQueryVoSingle.setHdEndDate(hdQueryVo.getHdEndDate());
        hdQueryVoSingle.setHdStatus(hdQueryVo.getHdStatus());
        hdQueryVoSingle.setHdImage(hdQueryVo.getHdImage());
        hdQueryVoSingle.setHdNumber(hdQueryVo.getHdNumber());
        hdQueryVoSingle.setGmtCreate(hdQueryVo.getGmtCreate());
        hdQueryVoSingle.setGmtModified(hdQueryVo.getGmtModified());
        hdQueryVoSingle.setUserId(hdQueryVo.getUserId());
        if (hdQueryVo.getHdType().equals(0)) {
            hdQueryVoSingle.setHdJoinUsers(onlineWorksMapper.getOnlineJoinUsers(hdQueryVo.getHdId()));
        } else {
            hdQueryVoSingle.setHdJoinUsers(offlineUsersMapper.getOfflineJoinUsers(hdQueryVo.getHdId()));
        }
        hdQueryVos.add(hdQueryVoSingle);
    }
    // 加工后的数据放入新的pageinfo
    target.setList(hdQueryVos);

    return target;
}

参考资料:

https://apidoc.gitee.com/free/Mybatis_PageHelper/

https://blog.csdn.net/shanglezeichaun/article/details/105039460

原文链接:https://blog.csdn.net/qq_35080796/article/details/105508744

版权声明:本文为CSDN博主「He Ain't Hero」的原创文章,遵循CC 4.0 BY-SA版权协议,转载请附上原文出处链接及本声明。

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posted @ 2021-06-04 19:12  Java技术栈  阅读(88)  评论(0编辑  收藏  举报