Inserting a POJO with a JsonNode field into MongoDB using Java driver

问题

Im using Mongo Java driver 3.7

This is my POJO(with getters and setters) -

public class Sample{
    public int field1;
    public JsonNode field2;
}

Im using the below code to insert an object of Sample into MongoDB.

MongoCollection<Sample> myCollection = database.getCollection("myCollection",Sample.class);
ObjectMapper mapper = new ObjectMapper();
    Sample obj = new Sample();
    obj.setField1(1);
    String sampleJSON = "{ \"key\": \"value\" }";
    obj.setField2(mapper.readTree(sample));

myCollection.insertOne(obj);

Seen Output: (JsonNode field is empty)

{
    "_id" : ObjectId("5afbff8a8f621e1e328a8c4e"),
    "field1" : 1
    "field2" : [
                 [ ]
               ],
}

Note: In debug mode, it is clear that the JsonNode is created with proper data. But insert is misbehaving. I guess I'm missing something here. Any leads appreciated.

Update: I tried writing a custom codec for JsonNode class, but it is never being used by mongo. This is my codec code -

@Slf4j
public class JsonNodeCodec implements CollectibleCodec<JsonNode> {
    @Inject
    private ObjectMapper objectMapper;

    @Override
    public JsonNode generateIdIfAbsentFromDocument(JsonNode jsonNode) {
        return null;
    }

    @Override
    public boolean documentHasId(JsonNode jsonNode) {
        return false;
    }

    @Override
    public BsonValue getDocumentId(JsonNode jsonNode) {
        return null;
    }

    @Override
    public JsonNode decode(BsonReader reader, DecoderContext decoderContext) {
        String task = reader.readString();
        JsonNode node = objectMapper.readTree(task);
        return node;
    }

    @Override
    public void encode(BsonWriter writer, JsonNode jsonNode, EncoderContext encoderContext) {
        writer.writeString(jsonNode.toString());
    }

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

And I'm registering the codec like this -

Codec<JsonNode> jsonNodeCodec = new JsonNodeCodec();
CodecRegistry codecRegistry = CodecRegistries.fromRegistries(com.mongodb.MongoClient.getDefaultCodecRegistry(),
            CodecRegistries.fromCodecs(jsonNodeCodec),
            CodecRegistries.fromProviders(PojoCodecProvider.builder().automatic(true).build())
    );

PS: Other codecs registered for custom POJOs are working fine. But this codec is never being used to encode/decode JSON objects

回答1:

I was facing the same issue here and resolved using ObjectMapper.

Use below:

ObjectMapper mapper =   new ObjectMapper();
Map inputMap        =   mapper.convertValue(jsonNode, Map.class);

来源：https://stackoverflow.com/questions/50368001/inserting-a-pojo-with-a-jsonnode-field-into-mongodb-using-java-driver

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json

mongodb

jackson

mongo-java-driver