日常踩坑

測(cè)試說(shuō)這個(gè)分頁(yè)總條數(shù)total不對(duì),總是等于傳入的pageSize大小,一臉懵逼,看下庫(kù)里確實(shí)不止這些數(shù)量

開始看代碼....
一直不相信這種簡(jiǎn)單的操作代碼有問(wèn)題....

說(shuō)明:就是一個(gè)列表查詢,返回的時(shí)候需要拿到數(shù)據(jù)進(jìn)行一些轉(zhuǎn)換封裝另外一個(gè)對(duì)象返回出去

看上去一切很正常的操作,能看出問(wèn)題嗎?

       //1.開啟分頁(yè)
         PageHelper.startPage(purchase.getPageNum(), purchase.getPageSize());

        //2.查數(shù)據(jù)
        List<TGmShoesCardExchangePurchaseRecord> list = tGmShoesCardExchangePurchaseRecordMapper.selectByExample(example);

        PageInfo<TGmShoesCardExchangePurchaseRecord> pageInfo = new PageInfo<>(list);
        //3.查到數(shù)據(jù)進(jìn)行轉(zhuǎn)換封裝返回
        List<CardExchangePurchaseDTO> collect = list.stream().map(record -> {
            CardExchangePurchaseDTO info = new CardExchangePurchaseDTO();
            BeanUtils.copyProperties(record, info);
            JSONObject jsonObject = JSON.parseObject((String) record.getSnapShot());
            info.setExchangeTime(record.getCreateTime().getTime());
            info.setSkuValue(jsonObject.getString("skuValue"));
            info.setReceiverName(jsonObject.getString("receiverName"));
            info.setReceiverPhone(jsonObject.getString("receiverPhone"));
            info.setAddress(jsonObject.getString("address"));
            return info;
        }).collect(Collectors.toList());

        //4.返回?cái)?shù)據(jù)
        return new PageInfo<>(collect);

看出來(lái)了嗎?

開啟分頁(yè)的時(shí)候是對(duì)數(shù)據(jù)層對(duì)象進(jìn)行查詢?nèi)缓髸?huì)返回一個(gè)Page對(duì)象,這個(gè)page設(shè)置了一些分頁(yè)的屬性
Page<Object> page = PageHelper.startPage(purchase.getPageNum(), purchase.getPageSize());

查詢數(shù)據(jù)庫(kù)
List<TGmShoesCardExchangePurchaseRecord> list = tGmShoesCardExchangePurchaseRecordMapper.selectByExample(example)
如果不轉(zhuǎn)換的話,應(yīng)該是將這個(gè)查到的對(duì)象直接放到PageInfo構(gòu)造器中返回
return new PageInfo<>(list)

看下new PageInfo()構(gòu)造函數(shù)源碼

 public PageInfo(List<T> list) {
        this(list, 8);
    }

//看下this方法
public PageInfo(List<T> list, int navigatePages) {
        this.isFirstPage = false;
        this.isLastPage = false;
        this.hasPreviousPage = false;
        this.hasNextPage = false;

      //重點(diǎn),如果list是屬于Page對(duì)象,那分頁(yè)信息從這個(gè)Page對(duì)象里獲取,沒(méi)問(wèn)題的
        if (list instanceof Page) {
            Page page = (Page)list;
            this.pageNum = page.getPageNum();
            this.pageSize = page.getPageSize();
            this.pages = page.getPages();
            this.list = page;
            this.size = page.size();
            this.total = page.getTotal();
            if (this.size == 0) {
                this.startRow = 0;
                this.endRow = 0;
            } else {
                this.startRow = page.getStartRow() + 1;
                this.endRow = this.startRow - 1 + this.size;
            }
      //這里,如果是新建的一個(gè)List(因?yàn)槲疫M(jìn)行數(shù)據(jù)轉(zhuǎn)換,這個(gè)List是新建的屬于Collection),所以分頁(yè)屬性
    //直接以list.size()去進(jìn)行判斷,看this.total=list.size(); 并不是數(shù)據(jù)庫(kù)的實(shí)際總條數(shù)
        } else if (list instanceof Collection) {
            this.pageNum = 1;
            this.pageSize = list.size();
            this.pages = this.pageSize > 0 ? 1 : 0;
            this.list = list;
            this.size = list.size();
            this.total = (long)list.size();
            this.startRow = 0;
            this.endRow = list.size() > 0 ? list.size() - 1 : 0;
        }

        if (list instanceof Collection) {
            this.navigatePages = navigatePages;
            this.calcNavigatepageNums();
            this.calcPage();
            this.judgePageBoudary();
        }

    }

那一般我們需要拿到數(shù)據(jù)還需要進(jìn)行處理,這里只針對(duì)不對(duì)數(shù)據(jù)進(jìn)行過(guò)濾篩選,只轉(zhuǎn)換,可以進(jìn)行重新設(shè)值

  PageHelper.startPage(purchase.getPageNum(), purchase.getPageSize());

        List<TGmShoesCardExchangePurchaseRecord> list = tGmShoesCardExchangePurchaseRecordMapper.selectByExample(example);

    
        //這邊先組裝PageInfo
        PageInfo<TGmShoesCardExchangePurchaseRecord> pageInfo = new PageInfo<>(list);

        List<CardExchangePurchaseDTO> collect = list.stream().map(record -> {
            CardExchangePurchaseDTO info = new CardExchangePurchaseDTO();
            BeanUtils.copyProperties(record, info);
            JSONObject jsonObject = JSON.parseObject((String) record.getSnapShot());
            info.setExchangeTime(record.getCreateTime().getTime());
            info.setSkuValue(jsonObject.getString("skuValue"));
            info.setReceiverName(jsonObject.getString("receiverName"));
            info.setReceiverPhone(jsonObject.getString("receiverPhone"));
            info.setAddress(jsonObject.getString("address"));
            return info;
        }).collect(Collectors.toList());

        //踩坑,分頁(yè)后數(shù)據(jù)要組裝轉(zhuǎn)換,分頁(yè)信息需要重新設(shè)置,不然會(huì)導(dǎo)致總頁(yè)數(shù)=list.size()
        //將需要轉(zhuǎn)換封裝的類new一個(gè)出來(lái),下面進(jìn)行屬性copy重新設(shè)值
        PageInfo<CardExchangePurchaseDTO> page = new PageInfo<>(collect);
        BeanUtils.copyProperties(pageInfo,page);
        page.setList(collect);
        return page;