feat(gen2-migration): support overriding default resolvers

[dgandhi62]

Input

Query.listBoards.req.vtl

## [Start] Custom List Request - Override to cap results at 50. **
#set( $args = $util.defaultIfNull($ctx.stash.transformedArgs, $ctx.args) )
#set( $limit = $util.defaultIfNull($args.limit, 50) )
## Cap the limit at 50 to keep the board list manageable
#if( $limit > 50 )
  #set( $limit = 50 )
#end
#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 )
#end
$util.toJson($ListRequest)
## [End] Custom List Request. **

Query.listBoards.res.vtl

## [Start] Custom ResponseTemplate - Prepend emoji to board names to prove override is active. **
#if( $ctx.error )
  $util.error($ctx.error.message, $ctx.error.type)
#end

## Add a pin emoji prefix to each board name so it's visible on the frontend
#foreach( $item in $ctx.result.items )
  #if( !$item.name.startsWith("📌 ") )
    $util.qr($item.put("name", "📌 $item.name"))
  #end
#end

$util.toJson($ctx.result)
## [End] Custom ResponseTemplate. **

Output

backend.ts

const __dirname = dirname(fileURLToPath(import.meta.url));
const resolversDir = join(__dirname, 'data/resolvers');
const resolverFiles = readdirSync(resolversDir).filter(
  (f) => f.endsWith('.req.vtl') || f.endsWith('.res.vtl')
);
for (const file of resolverFiles) {
  const parts = file.replace('.req.vtl', '').replace('.res.vtl', '').split('.');
  const [typeName, fieldName] = parts;
  const isRequest = file.endsWith('.req.vtl');
  const functionId = `${typeName}${
    fieldName.charAt(0).toUpperCase() + fieldName.slice(1)
  }DataResolverFn`;
  const pipelineFunction =
    backend.data.resources.cfnResources.cfnFunctionConfigurations[functionId];
  if (pipelineFunction) {
    const templatePath = join(resolversDir, file);
    const vtlTemplate = new assets.Asset(backend.data, `VTLTemplate-${file}`, {
      path: templatePath
    });
    if (isRequest) {
      pipelineFunction.requestMappingTemplateS3Location = vtlTemplate.s3ObjectUrl;
    } else {
      pipelineFunction.responseMappingTemplateS3Location = vtlTemplate.s3ObjectUrl;
    }
  }
}