Formatting DynamoDB data to normal JSON in Typescript and AWS Lambda

Question

I am retrieving data from DynamoDB using a query and I get the following returned:

[{"serviceUserId":{"S":"123456789"},"createdDate":{"S":"11-12-2021"}}]

The DynamoDB JSON format has the type in in which I am trying to get rid of by converting to a normal JSON format. I have tried using the AWS.DynamoDB.Converter.unmarshall but I am getting an error in my code:

Argument of type 'ItemList' is not assignable to parameter of type "AttributeMap".
  Index signature for type 'string' is missing in type "AttributeMap[]".

Here is my code:

                 if (result.Count > 0) {
                     const newImage = AWS.DynamoDB.Converter.unmarshall(
                        result.Items
                         )
                   console.log('new Image: ' + JSON.stringify(newImage));
                    resolve(newImage);
                 } else { 
                     console.log('No record found');
                     reject(err);
                 }

If I remove the [] brackets in the DynamoDB JSON then it is converted successfully, but obviously I cannot do this in my program as the brackets are there for a reason!

Does anyone know how to convert my JSON file to a format that unmarshall will accept?

result and result.items is '[object Object]' and when I stringify it I get '[{"serviceUserId":{"S":"123456789"},"createdDate":{"S":"11-12-2021"}}]' — Darren
– Darren, Commented Dec 17, 2021 at 17:21

fedonev · Accepted Answer · 2021-12-17 17:34:25Z

9

Map through the items and unmarshal one by one. (un)marshal accepts an object type, not an array.

import { marshall, unmarshall } from '@aws-sdk/util-dynamodb';  // SDK V3, but worked the same in V2

(() => {
  const items = [{ serviceUserId: { S: '123456789' }, createdDate: { S: '11-12-2021' } }];
  
  // from DynamoDB JSON
  const unmarshalled = items.map((i) => unmarshall(i));

  // make the return trip back to DynamoDB JSON
  const marshalled = unmarshalled.map((i) => marshall(i));
})();

answered Dec 17, 2021 at 17:34

fedonev

26.1k2 gold badges43 silver badges60 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Darren Over a year ago

Thanks - I shall give it a test a bit later but it all seems to make sense so hopefully it will work!

Darren Over a year ago

Unfortunately, this didn't quite work as my items variable has strings: '[{"serviceUserId":{"S":"123456789"},"createdDate":{"S":"11-12-2021"}}]' and yours was an object: 'const items = [{ serviceUserId: { S: '123456789' }, createdDate: { S: '11-12-2021' } }];' Unmarshall does not accept strings.

Darren Over a year ago

In addition, the DynamoDB data could have multiple items returned: '[{"serviceUserId":{"S":"123456789"},"createdDate":{"S":"11-12-2021"}},{"serviceUserId":{"S":"123456790"},"createdDate":{"S":"11-12-2021"},{"serviceUserId":{"S":"123456791"},"createdDate":{"S":"11-12-2021"}}]'

Darren Over a year ago

Any ideas to solve this?

fedonev Over a year ago

Convert your string into JSON with JSON.parse. Parsing will fail, however, if the string is not proper JSON. The multiple items string in your comment won't parse because the second element is missing a closing bracket. The answer will handle an array of items. That's what map does.

|

Collectives™ on Stack Overflow

Formatting DynamoDB data to normal JSON in Typescript and AWS Lambda

1 Answer 1

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related