An example, a table with a column counter with only 1 row. I want to update this row's counter value based on its current value.

Say if counter is >= 10, set it to 0, otherwise counter . How to achieve this if else clause in TransactWrite?

I can't have two actions in one transaction because Documentation states that it does not allow more than 1 action on the same item.

And of course, the reason I use TransactWrite is because there will be multiple lambda doing this task in parallel.

CodePudding user response：

You cannot do it in one request, transactional or otherwise.

You can get the item, decide what to do, and then update the item in a second request accordingly. You’ll want to keep a version number or timestamp attribute to make sure the item hasn’t changed between the read and write, and use a condition expression to fail if it has.

That’s a common idiom: https://dynobase.dev/dynamodb-locking/

CodePudding user response：

You can't do it the way you like, because if/else is not supported in transactions. There is however a simpler solution.

Just Update the item and increment the counter. Whenever you read the value, you take the counter value modulo 10, and you get the desired behavior, e.g. 123 % 10 = 3 or 10 % 10 = 0.