CODEWITHSUNDEEP
javamongodb
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Reputation: 789

Max value of a field with mongo-java-driver

I want to get max value of date field for whole collection 4programmers.

In mongo shell I can write:

db.getCollection("4programmers").aggregate([
    {
        $group:
        {
            _id: null,
            max : {$max:  "$date"}
        }
    }
])

and it returns a document with the date ISODate("2017-10-20T17:12:37.000+02:00") but when I write in java:

Date d = collection.aggregate(
                Arrays.asList(
                        Aggregates.group("$date", Accumulators.max("maxx", "$date"))
                        )
                ).first().getDate("maxx");
        System.out.println(d);

as a result I get: Fri Oct 20 00:44:50 CEST 2017

May something is wrong with first()?

Upvotes: 1

Views: 3208

Answers (1)

Vasyl Sarzhynskyi
Vasyl Sarzhynskyi

Reputation: 3955

First argument of Aggregates.group should be null instead of "$date" (it's actually _id: null). So code should look like:

Date d = collection.aggregate(
                Arrays.asList(
                        Aggregates.group(null, Accumulators.max("maxx", "$date"))
                        )
                ).first().getDate("maxx");

or you can do the same without Aggregates class:

collection.aggregate(asList(new Document("$group", new Document("_id", null)
                .append("max", new Document("$max", "$date")))))
                .first().getDate("max");

Upvotes: 2

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