Java - Mapping POJOs

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git clone https://github.com/mongodb-developer/java-quick-start

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{
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    "_id": {
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        "$oid": "56d5f7eb604eb380b0d8d8ce"
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    },
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    "student_id": {
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        "$numberDouble": "0"
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    },
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    "scores": [{
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        "type": "exam",
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        "score": {
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            "$numberDouble": "78.40446309504266"
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        }
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    }, {
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        "type": "quiz",
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        "score": {
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            "$numberDouble": "73.36224783231339"
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        }
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    }, {
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        "type": "homework",
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        "score": {
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            "$numberDouble": "46.980982486720535"
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        }
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    }, {
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        "type": "homework",
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        "score": {
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            "$numberDouble": "76.67556138656222"
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        }
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    }],
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    "class_id": {
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        "$numberDouble": "339"
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    }
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}

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package com.mongodb.quickstart.models;
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// imports
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public class Grade {
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    private ObjectId id;
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    @BsonProperty(value = "student_id")
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    private Double studentId;
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    @BsonProperty(value = "class_id")
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    private Double classId;
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    private List<Score> scores;
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    // getters and setters with builder pattern
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    // toString()
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    // equals()
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    // hashCode()
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}

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package com.mongodb.quickstart.models;
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import java.util.Objects;
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public class Score {
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    private String type;
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    private Double score;
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    // getters and setters with builder pattern
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    // toString()
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    // equals()
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    // hashCode()
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}

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ConnectionString connectionString = new ConnectionString(System.getProperty("mongodb.uri"));

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CodecRegistry pojoCodecRegistry = fromProviders(PojoCodecProvider.builder().automatic(true).build());

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CodecRegistry codecRegistry = fromRegistries(MongoClientSettings.getDefaultCodecRegistry(),
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                                             pojoCodecRegistry);

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MongoClientSettings clientSettings = MongoClientSettings.builder()
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                                                        .applyConnectionString(connectionString)
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                                                        .codecRegistry(codecRegistry)
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                                                        .build();

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try (MongoClient mongoClient = MongoClients.create(clientSettings)) {
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    MongoDatabase db = mongoClient.getDatabase("sample_training");
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    MongoCollection<Grade> grades = db.getCollection("grades", Grade.class);
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    [...]
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}

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Grade newGrade = new Grade().setStudent_id(10003d)
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                            .setClass_id(10d)
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                            .setScores(List.of(new Score().setType("homework").setScore(50d)));
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grades.insertOne(newGrade);

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Grade grade = grades.find(eq("student_id", 10003d)).first();
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System.out.println("Grade found:\t" + grade);

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List<Score> newScores = new ArrayList<>(grade.getScores());
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newScores.add(new Score().setType("exam").setScore(42d));
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grade.setScores(newScores);
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Document filterByGradeId = new Document("_id", grade.getId());
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FindOneAndReplaceOptions returnDocAfterReplace = new FindOneAndReplaceOptions()
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                                                     .returnDocument(ReturnDocument.AFTER);
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Grade updatedGrade = grades.findOneAndReplace(filterByGradeId, grade, returnDocAfterReplace);
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System.out.println("Grade replaced:\t" + updatedGrade);

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System.out.println(grades.deleteOne(filterByGradeId));

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package com.mongodb.quickstart;
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import com.mongodb.ConnectionString;
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import com.mongodb.MongoClientSettings;
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import com.mongodb.client.MongoClient;
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import com.mongodb.client.MongoClients;
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import com.mongodb.client.MongoCollection;
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import com.mongodb.client.MongoDatabase;
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import com.mongodb.client.model.FindOneAndReplaceOptions;
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import com.mongodb.client.model.ReturnDocument;
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import com.mongodb.quickstart.models.Grade;
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import com.mongodb.quickstart.models.Score;
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import org.bson.codecs.configuration.CodecRegistry;
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import org.bson.codecs.pojo.PojoCodecProvider;
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import org.bson.conversions.Bson;
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import java.util.ArrayList;
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import java.util.List;
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import static com.mongodb.client.model.Filters.eq;
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import static org.bson.codecs.configuration.CodecRegistries.fromProviders;
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import static org.bson.codecs.configuration.CodecRegistries.fromRegistries;
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public class MappingPOJO {
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    public static void main(String[] args) {
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        ConnectionString connectionString = new ConnectionString(System.getProperty("mongodb.uri"));
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        CodecRegistry pojoCodecRegistry = fromProviders(PojoCodecProvider.builder().automatic(true).build());
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        CodecRegistry codecRegistry = fromRegistries(MongoClientSettings.getDefaultCodecRegistry(), pojoCodecRegistry);
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        MongoClientSettings clientSettings = MongoClientSettings.builder()
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                                                                .applyConnectionString(connectionString)
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                                                                .codecRegistry(codecRegistry)
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                                                                .build();
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        try (MongoClient mongoClient = MongoClients.create(clientSettings)) {
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            MongoDatabase db = mongoClient.getDatabase("sample_training");
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            MongoCollection<Grade> grades = db.getCollection("grades", Grade.class);
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            // create a new grade.
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            Grade newGrade = new Grade().setStudentId(10003d)
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                                        .setClassId(10d)
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                                        .setScores(List.of(new Score().setType("homework").setScore(50d)));
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            grades.insertOne(newGrade);
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            System.out.println("Grade inserted.");
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            // find this grade.
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            Grade grade = grades.find(eq("student_id", 10003d)).first();
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            System.out.println("Grade found:\t" + grade);
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            // update this grade: adding an exam grade
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            List<Score> newScores = new ArrayList<>(grade.getScores());
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            newScores.add(new Score().setType("exam").setScore(42d));
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            grade.setScores(newScores);
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            Bson filterByGradeId = eq("_id", grade.getId());
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            FindOneAndReplaceOptions returnDocAfterReplace = new FindOneAndReplaceOptions().returnDocument(ReturnDocument.AFTER);
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            Grade updatedGrade = grades.findOneAndReplace(filterByGradeId, grade, returnDocAfterReplace);
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            System.out.println("Grade replaced:\t" + updatedGrade);
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            // delete this grade
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            System.out.println("Grade deleted:\t" + grades.deleteOne(filterByGradeId));
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        }
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    }
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}

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mvn compile exec:java -Dexec.mainClass="com.mongodb.quickstart.MappingPOJO" -Dmongodb.uri="mongodb+srv://USERNAME:PASSWORD@cluster0-abcde.mongodb.net/test?w=majority"