DynamoDB based on condition on Table A write to Table B

To achieve your goal of conditionally writing to Table B based on the rule version in Table A in DynamoDB, using TransactWriteItems is a suitable approach.

Here's how you can implement this:

• Your Lambda function should evaluate the rule in Table A and prepare to write the result to Table B. As part of the transaction, you need to include a condition check on the rule version in Table A.
• DynamoDB supports conditional writes using condition expressions. These expressions can check if certain attribute values in the item match what you expect them to be at the time of the request. For example, you can specify that the write operation to Table B should only occur if the version ID in Table A matches the one evaluated by your Lambda function​​.
• In your TransactWriteItems call, you will have an array of TransactWriteItem objects. This will include the write operation to Table B and a ConditionCheck on Table A to verify the version ID. Remember that all operations within a TransactWriteItems call must succeed for the transaction to be committed. If any operation fails (such as the condition check on Table A), the entire transaction is rolled back.

Let me know if you have any further questions to discuss.

Regards!

*Edit: Removed PII—Alex L