Write Codec for embedded documents in mongodb-java-driver

Question

I am using mongo-java-driver in my application to read and write data to mongodb.

I have classes like this -

public A{
    private String a;
    //Getters & Setters
}

public class B{
    private String b;
    private List<A> a;
    //Getters & Setters
}

public class C{
    private String c;
    private B b;
    //Getters & Setters
}

I have created Codec for the classes C like this -

public class CCodec implements Codec<C> {

    private Codec<Document> documentCodec;

    public CCodec(CodecRegistry registry) {
        documentCodec = registry.get(Document.class);
    }

    @Override
    public void encode(BsonWriter writer, C c, EncoderContext context)     {
        Document document = new Document();
        document.put("c",c.getC());
        document.put("b",c.getB());
        documentCodec.encode(writer, document, context);
    }
}

Codec for class B -

public class BCodec implements Codec<B> {

        private Codec<Document> documentCodec;

        public CCodec(CodecRegistry registry) {
            documentCodec = registry.get(Document.class);
        }

        @Override
        public void encode(BsonWriter writer, B b, EncoderContext context)     {
            writer.writeStartDocument();
            writer.writeString("b",b.getB());
            //How to encode A Here
            writer.writeEndDocument();
        }
    }

I can not do encoding in BCodec as i did for CCodec because when i say

Document document = new Document();

It creates a new document but i wan't to have it embedded in Document C.

Now the question is how do i encode field a of type List in B class? See encode method of BCodec class. Needless to say i have added all the Codec in CodecProvider.

Any help is appreciated.

Naman · Accepted Answer · 2017-06-07 04:26:57Z

1

You can try using the DocumentCodec.encode method as follows -

@Override
public void encode(BsonWriter writer, B b, EncoderContext context) {
    org.bson.Document bsonDocument = new org.bson.Document();
    List<A> a = B.getA();
    bsonDocument.put("a", a);
    ...
    documentCodec.encode(writer, bsonDocument, encoderContext);
}

and as you decode :

@Override
public B decode(BsonReader reader, DecoderContext decoderContext) {
    org.bson.Document bsonDocument = documentCodec.decode(reader, decoderContext);
    B b = new B();
    b.setA((List)bsonDocument.getString("a"));
    ...
    return b;
}

answered Jun 7, 2017 at 4:26

Naman

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2 Comments

Ravi Kumar Over a year ago

How is it different from one i have written above?

Naman Over a year ago

@RaviKumar //How to encode A Here in your code is what has been answered. how do i encode field a of type List in B class? is where I have casted the encoded A to a List while decoding the B.

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