Mongodb聚合查詢：經過文章的閱讀量，評論量，點贊量等計算出一個熱度值用於排序

spring data es實現方式：

TypedAggregation<Album> agg = Aggregation.newAggregation(
        Album.class,
        Aggregation.project("id","albumName","coverImgId","popular").and("countRead").plus("countComment").plus("countLike").as("polular"),
        Aggregation.sort(Sort.Direction.DESC,"popular"),
        Aggregation.skip (page),
        Aggregation.limit(pageSize));
AggregationResults<PoplularAlbumDto> results=mongoTemplate.aggregate(agg, PoplularAlbumDto.class);

解析：.project()裏可指定要查詢的字段，還可使用一些字段的加減乘除運算出一個新的字段，上面的是「countRead」,"countComment","countLIke"這幾個字段的和做爲一個新的字段「polular」，並按popular降序排序，skip表明頁碼，limit表明分頁大小；