fix(model-transformer) IndexName -> index in query list resolver

[atierian]

Description of changes

Renames invalid IndexName key to valid index for generated model list queries.

The VTL data resolver for DynamoDB data sources in generated model list queries contains a code path that (as far as I can tell) is never hit.

#if( !$util.isNull($ctx.stash.metadata.index) )
  #set( $ListRequest.IndexName = $ctx.stash.metadata.index )
#end

I'm confident it's never hit because IndexName is an invalid key to include in the request function evaluation for the only two DDB operations this resolver function can initiate -- Scan and Query. The correct key is index.

Mapping Document Structure

AppSync Documentation References

• Query
• Scan

The linked AppSync documentation shows that the correct key name for this purpose is index, not IndexName.

Query Mapping Document Structure

{
    "version" : "2017-02-28",
    "operation" : "Query",
    "query" : {
        "expression" : "some expression",
        "expressionNames" : {
            "#foo" : "foo"
        },
        "expressionValues" : {
            ":bar" : ... typed value
        }
    },
    "index" : "fooIndex", // <--- 👀 
    "nextToken" : "a pagination token",
    "limit" : 10,
    "scanIndexForward" : true,
    "consistentRead" : false,
    "select" : "ALL_ATTRIBUTES" | "ALL_PROJECTED_ATTRIBUTES" | "SPECIFIC_ATTRIBUTES",
    "filter" : {
        ...
    },
    "projection" : {
        ...
    }
}

Scan Mapping Document Structure

{
    "version" : "2017-02-28",
    "operation" : "Scan",
    "index" : "fooIndex", // <--- 👀 
    "limit" : 10,
    "consistentRead" : false,
    "nextToken" : "aPaginationToken",
    "totalSegments" : 10,
    "segment" : 1,
    "filter" : {
        ...
    },
    "projection" : {
        ...
    }
}

For completeness sake, here's the error message if ctx.stash.metadata.index exists and $ListRequest.IndexName is set.

{
  "data": {
    "listThings": null
  },
  "errors": [
    {
      "path": [
        "listThings"
      ],
      "data": null,
      "errorType": "MappingTemplate",
      "errorInfo": null,
      "locations": [
        {
          "line": 2,
          "column": 3,
          "sourceName": null
        }
      ],
      "message": "Unsupported element '$[IndexName]'."
    }
  ]
}

Q&A

If this code path is never hit, why are you making this change?

I'd like to use it 😄
For the conversation transformer, we use the model generated list query to surface conversation messages. It's important that message history be returned in sorted order. By fixing this issue, I can insert a simple resolver function into the existing list query pipeline to set ctx.stash.metadata.index.

Ok, but why is it IndexName now if that doesn't work?

As far as I can tell, it's been IndexName since this feat: transformer redesign PR in the aws-amplify/amplify-cli repo. I wasn't able to find any relevant commit or PR descriptions, or discussions from reviewers around this line. My assumptions are that IndexName was always incorrect, was added back then as a we might want this one day thing, and we've just never supported a code path that hits it.

It looks like this is the specific commit that added it back then.

I was unable to find anywhere in the transformer where ctx.stash.metadata.index is actually being set. Doing this exhaustively is hard though, so I can't make any assurances that it's not being done.

Model List Query Diff

## [Start] List Request. **
#set( $args = $util.defaultIfNull($ctx.stash.transformedArgs, $ctx.args) )
#set( $limit = $util.defaultIfNull($args.limit, 100) )
#set( $ListRequest = {
  "version": "2018-05-29",
  "limit": $limit
} )
#if( $args.nextToken )
  #set( $ListRequest.nextToken = $args.nextToken )
#end
#if( !$util.isNullOrEmpty($ctx.stash.authFilter) )
  #set( $filter = $ctx.stash.authFilter )
  #if( !$util.isNullOrEmpty($args.filter) )
    #set( $filter = {
  "and":   [$filter, $args.filter]
} )
  #end
#else
  #if( !$util.isNullOrEmpty($args.filter) )
    #set( $filter = $args.filter )
  #end
#end
#if( !$util.isNullOrEmpty($filter) )
  #set( $filterExpression = $util.parseJson($util.transform.toDynamoDBFilterExpression($filter)) )
  #if( $util.isNullOrEmpty($filterExpression) )
    $util.error("Unable to process the filter expression", "Unrecognized Filter")
  #end
  #if( !$util.isNullOrBlank($filterExpression.expression) )
    #if( $filterExpression.expressionValues.size() == 0 )
      $util.qr($filterExpression.remove("expressionValues"))
    #end
    #set( $ListRequest.filter = $filterExpression )
  #end
#end
#if( !$util.isNull($ctx.stash.modelQueryExpression) && !$util.isNullOrEmpty($ctx.stash.modelQueryExpression.expression) )
  $util.qr($ListRequest.put("operation", "Query"))
  $util.qr($ListRequest.put("query", $ctx.stash.modelQueryExpression))
  #if( !$util.isNull($args.sortDirection) && $args.sortDirection == "DESC" )
    #set( $ListRequest.scanIndexForward = false )
  #else
    #set( $ListRequest.scanIndexForward = true )
  #end
#else
  $util.qr($ListRequest.put("operation", "Scan"))
#end
#if( !$util.isNull($ctx.stash.metadata.index) )
-  #set( $ListRequest.IndexName = $ctx.stash.metadata.index )
+  #set( $ListRequest.index = $ctx.stash.metadata.index )
#end
$util.toJson($ListRequest)
## [End] List Request. **

CDK / CloudFormation Parameters Changed

Issue #, if available

Description of how you validated changes

• PR CI job
• E2E tests
• Lots of manual testing

Checklist

• PR description included
• yarn test passes
• E2E test run linked
• Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)
• New AWS SDK calls or CloudFormation actions have been added to relevant test and service IAM policies
• Any CDK or CloudFormation parameter changes are called out explicitly

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.