Dynamo DB Transactions

dynamodb-transactions.md

About DDB transactions: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/transactions.html

Rules of transactions:

1. You cannot have more than one operation in your transaction for a single item.

2. You cannot use the results of one operation as an input to another operation in the same transaction.

3. Aside from the uniqueness of the primary key, there is no enforced dependency (nor enforced non/anti-dependency) between any items in the same table.

4. There are no dependencies between items in different tables (such as a foreign key requirement) that DynamoDB enforces.

https://stackoverflow.com/questions/56958718/does-the-order-of-operations-in-a-transaction-matter

DynamoDB transaction example for updating Stock when creating Order

https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/transaction-example.html

DynamoDB transaction example for Checking Credits before making Purchase

https://aws.amazon.com/blogs/aws/new-amazon-dynamodb-transactions/

How to debug your custom VTL resolvers

1. Do amplify mock

• See section Local Debugging and Customizing VTL Resolvers in https://aws.amazon.com/blogs/mobile/amplify-framework-local-mocking/
• https://stackoverflow.com/questions/50608382/where-can-i-log-debug-velocity-template-language-vtl-in-aws-appsync

2. Do $util.error($MY_OBJECT) to view data in the graphql playground

Note: Amplify Mock / DynamoDB Local does not support Transactions

See: https://stackoverflow.com/questions/56708859/dynamodb-transactwriteitems-error-an-unknown-operation-was-requested/56709065

Video about DynamoDB Transactions and common use cases

https://www.youtube.com/watch?v=IgFvWaSQaeg