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From chunhui-shi <...@git.apache.org>
Subject [GitHub] drill issue #702: DRILL-5088: set default codec for toJson
Date Thu, 12 Jan 2017 08:30:57 GMT
Github user chunhui-shi commented on the issue:

    MongoGroupScan tries to read first record to guess record width. So this toJson is called
for only first record.
    Notice that MongoClient.getDefaultCodecRegistry() contains DBRefCodecProvider:
    Shown in MongoClient.java(In MongoClient.java):
        private static final CodecRegistry DEFAULT_CODEC_REGISTRY =
                fromProviders(asList(new ValueCodecProvider(),
                        new DBRefCodecProvider(),
                        new DocumentCodecProvider(new DocumentToDBRefTransformer()),
                        new DBObjectCodecProvider(),
                        new BsonValueCodecProvider(),
                        new GeoJsonCodecProvider()));
    but a default DocumentCodec constructor does not. And it was this constructor get called
if we don't set a codec for toJson function to use. The list of CodecProviders is shown in
DocumentCodec.java in MongoDb's code:
    public class DocumentCodec implements CollectibleCodec<Document> {
        private static final String ID_FIELD_NAME = "_id";
        private static final CodecRegistry DEFAULT_REGISTRY = fromProviders(asList(new ValueCodecProvider(),
                new BsonValueCodecProvider(),
                new DocumentCodecProvider()));

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