Tips for retrieving only the changes or updates from DynamoDB streams

Currently, I am faced with a scenario where I must comprehend the distinction between NEW_IMAGE and OLD_IMAGE on dynamoDB streams.

As per the information available at:

https://aws.amazon.com/blogs/database/dynamodb-streams-use-cases-and-design-patterns/

DynamoDB Streams offers various stream record viewpoints:

KEYS_ONLY—Consisting of only the key attributes of the modified item
NEW_IMAGE—Comprising the complete item after modification
OLD_IMAGE—Containing the complete item before being modified
NEW_AND_OLD_IMAGES—Showcasing both the new and old versions of the item

I am unable to subscribe for observing IMAGE_DIFFERENCE or similar events.

Hence, what would be the optimal approach to address this query? Kindly provide an example, preferably in JavaScript/TypeScript.

javascripttypescriptamazon-web-servicesamazon-dynamodbamazon-dynamodb-streams

Answer №1

One way to approach this is by monitoring NEW_AND_OLD_IMAGES and comparing them manually. If AWS were to introduce an IMAGE_DIFFERENCE feature, it would require a unique method of indicating deleted and added entries. However, implementing such functionality could potentially increase latency in the streams, making it less practical for various use cases.

Answer №2

To achieve the desired result, you can utilize the functions unmarshall and json-diff:

npm install json-diff

const { unmarshall } = require("@aws-sdk/util-dynamodb");
const jsonDiff = require('json-diff');

exports.handler = async (event) => {
    console.log(JSON.stringify(event));
    const dynamoDBEvent = event.Records[0].dynamodb;
    const newImage = unmarshall(dynamoDBEvent.NewImage);
    const oldImage = unmarshall(dynamoDBEvent.OldImage);
    const diff = jsonDiff.diffString(oldImage, newImage)
    console.log(diff);
    return 'completed';
};

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