AppSync wrong id for schema in DynamoDB

Question

I am using a graphql API with AppSync that receives post requests from a lambda function that is triggered by AWS IoT with sensor data in the following JSON format:

{ "scoredata": { "id": "240", "distance": 124, "timestamp": "09:21:11", "Date": "04/16/2022" } }

The lambda function uses this JSON object to perform a post request on the graphql API, and AppSync puts this data in DynamoDB to be stored. My issue is that whenever I parse the JSON object within my lambda function to retrieve the id value, the id value does not match with the id value stored in DynamoDB; appsync is seemingly automatically generating an id.

Here is a screenshot of the request made to the graphql api from cloudwatch:

Here is what DynamoDB is storing:

I would like to know why the id in DynamoDB is shown as 964a3cb2-1d3d-4f1e-a94a-9e4640372963" when the post request id value is "240" and if there is anything I can do to fix this.

Answer 1

I can’t tell for certain but i’m guessing that dynamo db schema is autogenerating the id field on insert and using a uuid as the id type. An alternative would be to introduce a new property like score_id to store this extraneous id.

Answer 2

If you are using amplify most likely the request mapping templates you are generating automatically identify the "id" field as a unique identifier to be generated at runtime.

I recommend you to take a look at your VTL request template, you will most likely find something like this:

$util.qr($context.args.input.put("id", $util.defaultIfNull($ctx.args.input.id, $util.autoId())))

Surely the self-generated id comes from $util.autoId()

Probably some older version of Amplify could omit the verification $util.defaultIfNull($ctx.args.input.id,... and always overwrite the id by self-generating it.