DynamoDB based on condition on Table A write to Table B

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I have a use-case where there is a rule db which stores rules and it's version id. A lambda evaluates the rule and write result to Table B. During the evaluation the rule can be updated in that case i want to previous write to fail. I want to check the rule version that got evaluated in Rule Table is the latest at the time of write. Can i achieve this via TransactWriteItems ?

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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

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