how to get sum of int array field in projection in spring data mongodb

Question

Sample Document from Collection

{
    "_id" : 2,
    "student" : "Ryan",
    "homework" : [
        5,
        6,
        5
    ],
    "quiz" : [
        8,
        8
    ],
    "extraCredit" : 8
}

Aggregation Query in mongodb

db.scores.aggregate([
     {
        $project : {
            _id:"$_id",
            hSum : { $sum: "$homework" },
            qSum : { $sum: "$quiz"},
        }
     }])

Output Of above aggregation query

{
    "_id" : 2,
    "hSum" : 16,
    "qSum" : 16
}

I want to convert above mongo query in spring-data format. I want to do aggregation with projectionOperations in spring data. how to write with projectionOperation ?

what have you tried so far? And also i think your expected output isnt correct. 5+6+5 = 16 and 8+8 =16 — pvpkiran
– pvpkiran, Commented Feb 14, 2018 at 8:04
i have tried this in mongo terminal. and it is giving shown output. query running fine. i just want to convert that query in spring-data format any help plz ? — Adarsh Patel
– Adarsh Patel, Commented Feb 14, 2018 at 8:21
Sry mistake in choosing wrong output. i have shown result of id:1 my mistake @pvpkiran — Adarsh Patel
– Adarsh Patel, Commented Feb 14, 2018 at 8:32
aggregate operation makes sens if you are doing over multiple documents. But if you are doing in a single document, it is better if you just read the document and do the calculation in your code — pvpkiran
– pvpkiran, Commented Feb 14, 2018 at 11:49

pvpkiran · Accepted Answer · 2018-02-14 15:58:55Z

4

This should work

MatchOperation matchOperation = match(Criteria.where("_id").is(2));

AggregationExpression homeworkExpression = AccumulatorOperators.Sum.sumOf("homework");
AggregationExpression quizExpression = AccumulatorOperators.Sum.sumOf("quiz");
ProjectionOperation projectionOperation = project("someId").and(homeworkExpression).as("hSum")
        .and(quizExpression).as("qSum");

Aggregation aggregation = newAggregation( matchOperation, projectionOperation);
AggregationResults<Result> results = mongoTemplate.aggregate(aggregation, "ScoresColletionName", Result.class);

You can create a class called Result like this to get the values

@Getter
@Setter
class Result {
    private int someId;
    private int hSum;
    private int qSum;
}

answered Feb 14, 2018 at 15:58

pvpkiran

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Wrong Over a year ago

how can i do this if what i have is an array of objects and I want the sum of a field of all of them?

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