dynamodb fill empty cells with previous value

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 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 docs.

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