MongoDB aggregation with Java driver

Question

I need your help for using MongoDB aggregation framework with java driver. I don\'t understand how to write my request, even with this documentation.

I want to get t

Answer 1

Here is a simple way to count employee by departmentId.. Details at: Aggregation using Java API

        Map empCountMap = new HashMap<>();

        AggregateIterable iterable = getMongoCollection().aggregate(Arrays.asList(
                new Document("$match",
                        new Document("active", Boolean.TRUE)
                                .append("region", "India")),
                new Document("$group",
                        new Document("_id", "$" + "deptId").append("count", new Document("$sum", 1)))));

        iterable.forEach(new Block() {
            @Override
            public void apply(final Document document) {
                empCountMap.put((Long) document.get("_id"), (Integer) document.get("count"));
            }
        });