是否可以使用 Spring 数据 MongoDB 聚合对数字进行舍入？

Question

我有以下聚合管道来计算嵌入评论的手机集合中评分最高的品牌。

public Document findTopRatedBrands(int minReviews, int results) {
        UnwindOperation unwindOperation = unwind("reviews");
        GroupOperation groupOperation = group("$brand").avg("$reviews.rating")
                        .as("avgRating").count().as("numReviews");
        MatchOperation matchOperation = match(new Criteria("numReviews").gte(minReviews));
        SortOperation sortOperation = sort(Sort.by(Sort.Direction.DESC, "avgRating",
                "numReviews"));
        LimitOperation limitOperation = limit(results);
        ProjectionOperation projectionOperation = project().andExpression("_id").as
                ("brand").andExpression("avgRating").as("rating").andExclude("_id")
                .andExpression("numReviews").as("reviews");
        Aggregation aggregation = newAggregation(unwindOperation, groupOperation, matchOperation,
                sortOperation, limitOperation, projectionOperation);
        AggregationResults<Phone> result = mongoOperations
                .aggregate(aggregation, "phones", Phone.class);
        return result.getRawResults();
    }

phones 集合中的文档示例如下：

{
    "_id": {
        "$oid": "61e1cc8f452d0aef89d9125f"
    },
    "brand": "Samsung",
    "name": "Samsung Galaxy S7",
    "releaseYear": 2016,
    "reviews": [{
        "_id": {
            "$oid": "61d4403b86913bee0245c171"
        },
        "rating": 2,
        "dateOfReview": {
            "$date": "2019-12-24T00:00:00.000Z"
        },
        "title": "Won't do that again.",
        "body": "I could not use with my carrier. Sent it back.",
        "username": "bigrabbit324"
    }]
} 

我想按 avgRating（四舍五入到小数点后一位）排序，其次按评论数排序。现在平均评分它没有四舍五入，所以它总是给出不同的值，所以我也不能按评论数量排序。我已经看过 ArithmeticOperators.Round 类，但如果可能的话，我不明白如何在此处包含它。

结果示例如下：

[Document{{brand=Nokia, rating=3.25, reviews=4}}] 

我希望评分为 3.2。

这适用于 Mongo Compass：

    $project: {
        _id: 0,
        brand: '$_id',
        rating: { $round: ['$avgRating', 1] }
    }

Answer 1

试试

ProjectionOperation roundAverageRating = Aggregation.project("avgRating", "numReviews")
    .and(ArithmeticOperators.Round.roundValueOf("avgRating").place(1))
    .as("avgRatingRounded");