hw3.java

/**
 * Copy and Paste this snippet and solve your homework 2.3 of Mongo course for Java Developers.
 * Remember to import all libraries before you use.
 * This project is handled by Maven so you have to use Maven too with the dependency of MongoJavaDriver
 *
 * Created By gegen07
 */
public class App {
    public static void main( String[] args ) {
        MongoClient client = new MongoClient("localhost", 27017);
        MongoDatabase db = client.getDatabase("students");
        MongoCollection<Document> grades = db.getCollection("grades");

        Bson filter = eq("type", "homework");
        Bson projection = fields(include("student_id", "score"));
        Bson sort = orderBy(ascending("student_id"), descending("score"));

        List<Document> cursor = grades.find(filter)
                .sort(sort)
                .projection(projection)
                .into(new ArrayList<Document>());

        removeLowest(grades, cursor);
    }

    private static void removeLowest(MongoCollection grades, List<Document> cursor) {
        ObjectId _id = null;
        Integer id;

        id = cursor.get(0).getInteger("student_id");

        for (Document doc: cursor) {
            int aux = doc.getInteger("student_id");
            if (id != aux) {
                id = doc.getInteger("student_id");
                grades.deleteOne(new Document("_id", _id));
            }
            _id = doc.getObjectId("_id");
        }
        grades.deleteOne(new Document("_id", _id));
    }
}