Formatting DynamoDB data to normal JSON in AWS Lambda

Question

I\'m using AWS Lambda to scan data from a DynamoDB table. This is what I get in return:

{
  \"videos\": [
    {
      \"fil         


        

Answer 1

If you need online editor try this

https://2json.net/dynamo

Answer 2

I think it's just a custom transformation exercise for each app. A simple conversion from DynamoDB's item format to you application format might look like this:

var response = {...} // your response from DynamoDB
var formattedObjects = response.videos.map(function(video) {
    return {
        "file": video.file.S,
        "id": video.id.S,
        "canvas": video.canvas.S
    };
});

If you want to build a generic system for this, you would have to handle DynamoDB's various AttributeValue types. A function like the one below would do the job, but I've left out the hard work of handling most of DynamoDB's more complex attribute value types:

function dynamoItemToPlainObj(dynamoItem) {
    var plainObj = {};
    for (var attributeName in dynamoItem) {
        var attribute = dynamoItem[attributeName];
        var attributeValue;
        for (var itemType in attribute) {
            switch (itemType) {
            case "S":
                attributeValue = attribute.S.toString();
                break;
            case "N":
                attributeValue = Number(attribute.N);
                break;
                // more attribute types...
            default:
                attributeValue = attribute[itemType].toString();
                break;
            }
        }
        plainObj[attributeName] = attributeValue;
    }
    return plainObj;
}    
var formattedObjects = response.videos.map(dynamoItemToPlainObj);

Answer 3

Here you can find gist which does that:

function mapper(data) {

let S = "S";
let SS = "SS";
let NN = "NN";
let NS = "NS";
let BS = "BS";
let BB = "BB";
let N = "N";
let BOOL = "BOOL";
let NULL = "NULL";
let M = "M";
let L = "L";

if (isObject(data)) {
    let keys = Object.keys(data);
    while (keys.length) {
        let key = keys.shift();
        let types = data[key];

        if (isObject(types) && types.hasOwnProperty(S)) {
            data[key] = types[S];
        } else if (isObject(types) && types.hasOwnProperty(N)) {
            data[key] = parseFloat(types[N]);
        } else if (isObject(types) && types.hasOwnProperty(BOOL)) {
            data[key] = types[BOOL];
        } else if (isObject(types) && types.hasOwnProperty(NULL)) {
            data[key] = null;
        } else if (isObject(types) && types.hasOwnProperty(M)) {
            data[key] = mapper(types[M]);
        } else if (isObject(types) && types.hasOwnProperty(L)) {
            data[key] = mapper(types[L]);
        } else if (isObject(types) && types.hasOwnProperty(SS)) {
            data[key] = types[SS];
        } else if (isObject(types) && types.hasOwnProperty(NN)) {
            data[key] = types[NN];
        } else if (isObject(types) && types.hasOwnProperty(BB)) {
            data[key] = types[BB];
        } else if (isObject(types) && types.hasOwnProperty(NS)) {
            data[key] = types[NS];
        } else if (isObject(types) && types.hasOwnProperty(BS)) {
            data[key] = types[BS];
        }
    }
}


return data;

function isObject(value) {
    return typeof value === "object" && value !== null;
}

}

https://gist.github.com/igorzg/c80c0de4ad5c4028cb26cfec415cc600

Answer 4

Actually you should use the unmarshall function from AWSJavaScriptSDK:

const AWS = require("aws-sdk");

exports.handler = function( event, context, callback ) {
  const newImages = event.Records.map(
        (record) => AWS.DynamoDB.Converter.unmarshall(record.dynamodb.NewImage)
  );
  console.log('Converted records', newImages);
  callback(null, `Success`);
}

Answer 5

AWS JavaScript SDK was recently updated with Document Client which does exactly what you need. Check the announce and usage examples here: http://blogs.aws.amazon.com/javascript/post/Tx1OVH5LUZAFC6T/Announcing-the-Amazon-DynamoDB-Document-Client-in-the-AWS-SDK-for-JavaScript

Answer 6

I know is a bit old but I had the same problem processing stream data from dynamoDB in node js lambda function. I used the proposed by @churro

import sdk and output converter

var AWS = require("aws-sdk");
var parse = AWS.DynamoDB.Converter.output;

use the parse function with a small hack

exports.handler = function( event, context, callback ) {
  var docClient = new AWS.DynamoDB.DocumentClient();
  event.Records.forEach((record) => {
        console.log(record.eventID);
        console.log(record.eventName);
        console.log('DynamoDB Record:', parse({ "M": record.dynamodb.NewImage }));
    });
  callback(null, `Successfully processed ${event.Records.length} records.`);
}

Hope it helps