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Amazon DynamoDB single-table design with AWS Step Functions

An example of how one might create APIs backed by Amazon API Gateway, AWS Step Functions while utilizing the Amazon DynamoDB as a data layer in single-table methodology.

Please note that this is only an example. I would suggest ensuring that every step in the state machine has some kind of Catch state defined for production usage.

The data model

The data model represents the 1:n relation between a cat and its owner. The owner can have multiple cats. The cat can have only a single owner.

Deployment

npm run install
npm run bootstrap
npm run deploy

Playing around

The API consist of four routes.

POST ${APIGW_URL}/owner
GET ${APIGW_URL}/owner/${OWNER_ID}
POST ${APIGW_URL}/owner/${OWNER_ID}/cat
GET ${APIGW_URL}/owner/${OWNER_ID}/cats

Learnings

Splitting strings is impossible with JsonPath. JsonPath is used in AWS Step Functions for expression evaluation.
- This might be especially limiting while overloading Amazon DynamoDB indexes.
- Consider storing the values you overload the indexes with as separate attributes. You should be able to retrieve them later on while performing various transformations.
On the other hand, concatenating values is relatively hassle-free. One has to use the States.Format intrinsic function.
When deploying with more complex indexing schemes, you will most likely need to employ an AWS Lambda function for data transformation – going from Amazon DynamoDB item to your API item.
- Such tools exist – like the Stedi Mappings that I've helped to build :)

WojciechMatuszewski/ddb-single-table-step-functions

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