I have the following aggregation pipeline to calculate the top rated brands from a collection of phones with their reviews embedded.

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();
    }

An example of document in the phones collection is this:

{
    "_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"
    }]
} 

I would like to sort by avgRating (rounded to the first decimal place), and secondly by the number of reviews. Now the average rating it's not rounded so it gives always different values, so I can't sort by number of reviews also. I have seen the ArithmeticOperators.Round class but I don't understand how to include it here if possible.

An example of result is the following:

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

I would like to have 3.2 as rating.

This works in Mongo Compass:

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

CodePudding user response：

try

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