How to use DynamoDBStreamEvent Trigger Lambda when only update certain attribute

Question

I use serverless framework to deploy cloudFormation. I want to trigger lambda to deleteObject on my S3 bucket after I update my DynamoDB Table with certain attribute, eg. my table has account, user, icon, I only want when I update icon, it trigger Lambda to delete my iconObject on S3 bucket.

As I read the documentation on AWS, it seems the eventName of dynamoDB stream Event only have three status, REMOVE, MODIFY, INSERT.

AWS Documentation » Amazon DynamoDB » API Reference » Data Types » Amazon DynamoDB Streams » Record Record

Could I do as below? But how do I know it update icon instead other attribute like account or user?

if (this._record.eventName === 'MODIFY' && this._record.NewImage!== this._record.OldImage ){
        return this._remove(this._record.dynamodb);
    }

Hi, can you have a look here please? stackoverflow.com/questions/70020731/… — user13067694
– user13067694, Commented Nov 18, 2021 at 13:31

Brian Winant · Accepted Answer · 2018-05-25 06:14:59Z

11

You are on the right track. If the DynamoDB StreamViewType is set to NEW_AND_OLD_IMAGES then when record.eventName === 'MODIFY', record.dynamodb.NewImage will contain the updated version of the item and record.dynamodb.OldImage will contain what the item was before the update. You could then inspect the 2 objects and look for changes in the fields you are interested in.

answered May 25, 2018 at 6:14

Brian Winant

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2 Comments

Heckflosse_230 Over a year ago

Ah!!!!!! Thanks @bwinant! Had a hard time figuring out what's NewImage and OldImage.

user13067694 Over a year ago

Hi, can you have a look here please? stackoverflow.com/questions/70020731/…

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