How to apply Aggregation on Projected data in Spring boot Mongo?

Question

I have a requirement, for say an Employee class which contains a field as joining date. So what I'm doing is

    Query query = new Query();
    query.addCriteria(Criteria.where("joiningdate").gte("").andOperator(where("joiningdate").lt("")));

    List<Employeeemployee> trainings = mongoTemplate.find(query, Employee.class);

So I filtered out required employees based on the given date range. Now I want to apply aggregation on the returned value to calculate for example total salary.

I looked into a couple of examples and StackOverflow questions too but did not find what I was looking for. So any help?

Answer 1

The first step is to query the eligible data, and then summarize the total salary through the $sum function

        Criteria criteria = Criteria.where("joiningdate").gt("").lt("");
        // Just specify the query field
        Aggregation aggregation = Aggregation.newAggregation(Aggregation.match(criteria), Aggregation.group("").sum("").as("totalSalary"));
        AggregationResults<Map> results = mongoTemplate.aggregate(aggregation, "", Map.class);
        Map map = results.getMappedResults().get(0);
        System.out.println(map.get("totalSalary"));