Unmarshalling DynamoDB Data in TypeScript AWS Lambda Functions

DynamoDB is a popular NoSQL database service provided by Amazon Web Services (AWS) and is often used in serverless applications such as AWS Lambda.

In this article, we will discuss how to easily unmarshall DynamoDB data in TypeScript AWS Lambda functions.

Unmarshalling is the process of converting DynamoDB data, which is typically in JSON format, into a JavaScript object that can be easily manipulated in your code.

This guide will walk you through the process of importing the necessary modules, defining a function to handle incoming DynamoDB events, and converting the data into JavaScript objects for further processing.

DynamoDB records are not standard JavaScript objects

Here the code for a lambda that processes DynamoDB Stream records:

import { DynamoDBStreamHandler } from "aws-lambda";

export const handler: DynamoDBStreamHandler = async (event) => {
  for (const record of event.Records) {
    if (record.dynamodb && record.dynamodb.NewImage) {
        const newImage = record.dynamodb.NewImage;
        console.log("New Image: %j", newImage);
    }
  }
};

The newImage object will have this form:

{
    "Message": {
        "S": "New item!"
    },
    "Id": {
        "N": "101"
    }
}

What if we want a standard JavaScript object?

How to unmarshall DynamoDB records

The AWS SDK provides the unmashall function to convert a DynamoDB record into a JavaScript object.

Here is how to use it:

import { DynamoDBStreamHandler } from "aws-lambda";
import {
  AttributeValue,
} from "@aws-sdk/client-dynamodb";
import { unmarshall } from "@aws-sdk/util-dynamodb";

export const handler: DynamoDBStreamHandler = async (event) => {
  for (const record of event.Records) {
    if (record.dynamodb && record.dynamodb.NewImage) {
        const newImage = unmarshall(
            record.dynamodb.NewImage as { [key: string]: AttributeValue }
        );
        console.log("New Image: %j", newImage);
    }
  }
};

The trick to use unmarshall with DynamoDB Stream record, is that we have to cast it to { [key: string]: AttributeValue }.

After unmarshalling the DynamoDB Stream record, newImage is a standard JavaScript object:

{
    "Message": "New item!",
    "Id": 101
}

Conclusion

In conclusion, unmarshalling DynamoDB data in TypeScript AWS Lambda functions is a simple process that allows developers to easily interact with DynamoDB data in their TypeScript applications.

By importing the necessary modules and using the unmarshall method provided by the AWS SDK for JavaScript in Node.js, developers can easily convert DynamoDB data into JavaScript objects for further processing.

Additionally, the AWS SDK also provides a marshall function that can be used to convert a JavaScript object into a format that can be saved to DynamoDB, which is useful when creating or updating items in the database.

By following the steps outlined in this article, developers can easily work with DynamoDB data in their TypeScript Lambda functions.