How to prevent creating a new item in UpdateItem if the item does not exist

Question

I am running an AWS Lambda service written in Node.js that interacts with a DynamoDB database. One of my methods performs an update (AWS.DynamoDB.DocumentClient().update) on

Answer 1

ConditionExpression is the way to go, but you can also use the attribute_exists function :

ConditionExpression: 'attribute_exists(userId)'

It will only update the line with the correct key and throw a ConditionalCheckFailedException if requested key doesn't exist.

The goal is more obvious and you can skip the extra userId binding.

ref : https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.OperatorsAndFunctions.html