Do some data computations with extending postDataLoad resolver

[ggorge-etiqa]

Amplify CLI Version

12.6.0

Question

In my model I have a field ExpDate that is an iso timestamp. I want that when I list my model a computated field isExpired is set to true if ExpDate > current timestamp. Following https://docs.amplify.aws/cli/graphql/custom-business-logic/#extend-amplify-generated-resolvers I'm assuming I can create a postDataLoad VTL for accomplish the job and do a simple if statement inside it. I'm also assuming that I need to implement this logic inside the res VTL, but I'm not sure how the req VTL should be. Any hints?

[AnilMaktala]

Hey @ggorge-etiqa 👋 , Thank you for your question. Does the field isExpired already exist in the model, or would you like to inject it when retrieving the list query?

[ggorge-etiqa]

Hi @AnilMaktala I thought that adding the field isExpired in the model as optional Boolean is not a bad idea but I'm open to suggestion. Atm I succesfully managed this behavior with a lambda datasource for the postDataLoad appsync function but I would be more happy to not call an external lambda for such small work.

[ggorge-etiqa]

I probably managed it to work without using a Lambda. This is the req VTL as we use a NONE_DS datasource as documented here: https://docs.aws.amazon.com/appsync/latest/devguide/resolver-mapping-template-reference-none.html

{
    "version": "2018-05-29",
    "payload": $util.toJson($context.prev.result)
}

This is my res VTL with custom logic:

## [Start] ResponseTemplate. **

#set($currentMillis = $util.time.nowEpochMilliSeconds())

#foreach($item in $ctx.result.items)
    #set($item.isExpired = false)

    #if($item.expirationDate)
        #set($expirationDateMillis = $util.time.parseISO8601ToEpochMilliSeconds($item.expirationDate))
        #if($expirationDateMillis < $currentMillis)
          #set($item.isExpired = true)
        #end    
    #else
        ## Handle missing expiration date
        $util.error("An error occurred: Missing expiration date for item: $item")
    #end

#end

$util.toJson($ctx.result)

## [End] ResponseTemplate. **

If you have any other suggestion I'm open to try, otherwise I can consider the issue closed.

[AnilMaktala]

Hey @ggorge-etiqa, I apologize for the delay. I have consulted with the Engineering team, and they have confirmed that this is the recommended approach to fulfill your use case.