nl.mvdb.mongodb.RemoveStudentsLowestScore.java Source code

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Here is the source code for nl.mvdb.mongodb.RemoveStudentsLowestScore.java

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/*
 * Copyright 2015 MongoDB, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package nl.mvdb.mongodb;

import static com.mongodb.client.model.Sorts.ascending;

import org.bson.Document;

import com.mongodb.MongoClient;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoCursor;
import com.mongodb.client.MongoDatabase;

public class RemoveStudentsLowestScore {
    public static void main(String[] args) {
        MongoClient client = new MongoClient();
        try {
            MongoDatabase database = client.getDatabase("students");
            MongoCollection<Document> collection = database.getCollection("grades");

            MongoCursor<Document> iterator = collection.find().sort(ascending("student_id", "score")).iterator();

            Integer lastStudentId = null;
            while (iterator.hasNext()) {
                Document gradingDoc = iterator.next();
                Integer studentId = gradingDoc.getInteger("student_id");
                if (!studentId.equals(lastStudentId)) {
                    lastStudentId = studentId;
                    System.out.println(lastStudentId);
                    collection.deleteOne(gradingDoc);
                }
            }

            System.out.println(collection.count());
        } finally {
            client.close();
        }
    }
}