DynamoDB - Object to AttributeValue

Question

I'm aware of DynamoDBMapper but in my case I can't use it because I don't know all the attributes beforehand.

I have a JSON and it's parsed to a map of objects by using Jackson parser:

Map<String, Object> userData = mapper.readValue(new File("user.json"), Map.class);

Looping through each attribute, how can I convert the value to AttributeValue given that DynamoDB AttributeValue supports Boolean, String, Number, Bytes, List, etc.

Is there an efficient way to do this? Is there a library for this already? My naive approach is to check if each value is of type Boolean/String/Number/etc. and then call the appropriate AttributeValue method, eg: new AttributeValue().withN(value.toString()) - which gives me long lines of if, else if

Answer 1

Finally figured out by looking at how AWS parses the JSON

Basically, this is the code:

    Item item = new Item().withJSON("document", jsonStr);
    Map<String,AttributeValue> attributes = InternalUtils.toAttributeValues(item);
    return attributes.get("document").getM();

Very neat.

Answer 2

Following is a simple solution which can be applied to convert any DynamoDB Json to Simple JSON.

//passing the reponse.getItems() 
public static Object getJson(List<Map<String,AttributeValue>> mapList) {
    List<Object> finalJson= new ArrayList();
    for(Map<String,AttributeValue> eachEntry : mapList) {
        finalJson.add(mapToJson(eachEntry));
    }
    return finalJson;
}


//if the map is null then it add the key and value(string) in the finalKeyValueMap
public static Map<String,Object> mapToJson(Map<String,AttributeValue> keyValueMap){
    Map<String,Object> finalKeyValueMap = new HashMap();
    for(Map.Entry<String, AttributeValue> entry : keyValueMap.entrySet()) 
    {
        if(entry.getValue().getM() == null) {
            finalKeyValueMap.put(entry.getKey(),entry.getValue().getS());
        }
        else {
            finalKeyValueMap.put(entry.getKey(),mapToJson(entry.getValue().getM()));
        }
    }
    return finalKeyValueMap;
}

This will produce your desired Json in the form of List<Map<String,Object>> which is subset of the object .

Answer 3

I used JacksonConverterImpl to convert JsonNode to Map<String, AttributeValue>

ObjectMapper objectMapper = new ObjectMapper();
JsonNode jsonNode = objectMapper.readValue(jsonString, JsonNode.class);
final JacksonConverter converter = new JacksonConverterImpl();
Map<String, AttributeValue> map = converter.jsonObjectToMap(jsonNode);

Hope this helps!

Thanks, Jay