CODEWITHSUNDEEP
aws-lambdaamazon-dynamodb
Steve
Steve

Reputation: 4681

How to prevent overwrites/duplicates in dynamoDB from triggering lambda

I have a DynamoDB that is getting data written to it from a java app

mapper.save(row, DynamoDBMapperConfig.builder().withSaveBehavior(SaveBehavior.CLOBBER).build());

I want to have a lambda trigger off of new items in the DDB so that their keys can be put onto SNS. However, if an item in DynamoDB is being overwritten (IE we received duplicate data) we do NOT want to do anything with it.

How to handle that? I control both the lambda and the code writing to DDB, but not the source of the data.

Upvotes: 1

Views: 1952

Answers (2)

NoSQLKnowHow
NoSQLKnowHow

Reputation: 4845

You need to have an IF, CASE, or something that looks at the stream record's eventName and if it is INSERT, which means new if I recall correctly, then it will run your code. If it is something like MODIFY, then it will not. There is an example in the DynamoDB documentation.

Upvotes: 1

Sarthak Jain
Sarthak Jain

Reputation: 2096

I don't think we can prevent the Lambda from being triggered when an item is overwritten in DynamoDB. But once the Lambda is triggered, we can identify if it's a new record or an existing record.

The input to the Lambda function will be a DynamoDBStreamEvent which contains an OldImage attribute. If that is present, it indicates that it's an existing record that got modified. In this case, we can just return from the Lambda without doing any processing.

Also, the event contains the entire snapshot before and after the insert in the OldImage and NewImage attributes. So we can also check whether some other attribute value has changed or not to decide whether it's an overwrite.

Upvotes: 2

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