dynamodb fill empty cells with previous value

Question

Hi
I've been collecting data from IoT core and transfer it to aws dynamodb for storing the data. if the values didn't change the mqtt will receive an empty string were the cells remains empty. is their a way to fill the empty cells with their previous values? Or should i configure that on the mqtt part. Or can i remove the empty cells somehow?

Thanks!

Leeroy Hannigan · Answer

Its not clear from your question, but I believe you are calling `PutItem` with only select attributes, as `PutItem` is a complete overwrite of your data, you are deleting other attributes which you wish to maintain.

[PutItem](https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_PutItem.html) docs.

To overcome that, you should use `UpdateItem` which will only update the attributed given in the payload. Furthermore, if the item does not exist it will act like a `PutItem` and write the new item.

[UpdateItem](https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_UpdateItem.html) docs.

MassimilianoAWS · Answer

Hi,

I assume that you are using one of the AWS IoT Core DynamoDB actions in a rule. Both actions use `PutItem` hence the behavior you observe. As Leeroy mentions, `UpdateItem` should be used, but you will need to pass the message to a Lambda function first.

An alternative is to use a `WHERE` clause in the rule to only execute the rule if the string is not empty.

Massimiliano

dynamodb fill empty cells with previous value

Relevant content