MongoDB 3.0 java driver Codec example - Codec class for the mapping the Grades bean

GradesCodec.java

package org.scratch;

import org.bson.BsonReader;
import org.bson.BsonString;
import org.bson.BsonValue;
import org.bson.BsonWriter;
import org.bson.Document;
import org.bson.codecs.Codec;
import org.bson.codecs.CollectibleCodec;
import org.bson.codecs.DecoderContext;
import org.bson.codecs.DocumentCodec;
import org.bson.codecs.EncoderContext;
import org.bson.types.ObjectId;

public class GradesCodec implements CollectibleCodec<Grades> {

	private Codec<Document> documentCodec;

	public GradesCodec() {
		this.documentCodec = new DocumentCodec();
	}

	public GradesCodec(Codec<Document> codec) {
		this.documentCodec = codec;
	}

	@Override
	public void encode(BsonWriter writer, Grades value,
			EncoderContext encoderContext) {
		Document document = new Document();

		ObjectId id = value.getId();
		Double score = value.getScore();
		Integer studentId = value.getStudentId();
		String type = value.getType();

		if (null != id) {
			document.put("_id", id);
		}

		if (null != score) {
			document.put("score", score);
		}

		if (null != studentId) {
			document.put("student_id", studentId);
		}
		if (null != type) {
			document.put("type", type);
		}

		documentCodec.encode(writer, document, encoderContext);

	}

	@Override
	public Class<Grades> getEncoderClass() {
		return Grades.class;
	}

	@Override
	public Grades decode(BsonReader reader, DecoderContext decoderContext) {
		Document document = documentCodec.decode(reader, decoderContext);
		System.out.println("document "+document);
		Grades grade = new Grades();

		grade.setId(document.getObjectId("_id"));

		grade.setStudentId(document.getInteger("student_id"));

		grade.setType(document.getString("type"));

		grade.setScore(document.getDouble("score"));
		
		return grade;
	}

	@Override
	public Grades generateIdIfAbsentFromDocument(Grades document) {
		return documentHasId(document) ? document.withNewObjectId() : document;
	}

	@Override
	public boolean documentHasId(Grades document) {
		return null == document.getId();
	}

	@Override
	public BsonValue getDocumentId(Grades document) {
		if (!documentHasId(document))
	    {
	        throw new IllegalStateException("The document does not contain an _id");
	    }
	 
	    return new BsonString(document.getId().toHexString());
	}
}

Shouldn't documentHasId return false if document.getId() is null?

Very helpful, thank you!

Shouldn't generateIdIfAbsentFromDocument return the document itself when it has an id, and document.withNewObjectId when it hasn't?

заебись!

This example got me on track, thank you. There are a few other ways I've see people try to do this that were a lot less clean. Some possible improvements to your example would be fixing the inverted generateIdIfAbsentFromDocument logic. It also doesn't throw an error if there is no Id. I read through the DocumentCodec class source and it was edifying. Also, if you add BsonTypeClassMap to your GradesCodecProvider constructor and pass that through to the GradesCodec constructor where they can be passed to the constructor of your DocumentCodec instance, per http://mongodb.github.io/mongo-java-driver/3.4/bson/codecs/#codecprovider, your Grades class (or other peoples classes), can have complex field types without a bunch of complex conversion logic in the GradesCodec. I implemented this and it ended up being very clean. I would share the code but it's not open source (company code). Thanks again.

Hi, this really helped me, thank you very much. However, I am struggling how to serialize/deserialize a Date field.
I have tried using the something like this in the Codec implementation:
Date timestamp = value.getTimestamp();

However, I still have null results.

Thanks man!

Thanks! Your example code helped me migrate my Codec from streaming based to document based.