I am working with the Apache Velocity Template Language (VTL) in AWS AppSync. In my request template I query an undefined amount of items with different elements. What I want to do in the response template is to transform the result into a JSON Object which I need later on for my BatchDeleteItem operation. This is how I solved it currently:
#set($deleteObject='{"Id" : { "S": "nodelete" },"Sk" : { "S": "nodelete" }}')
#set($replaceDeleteObject ="")
#set($separator="")
#foreach( $item in $ctx.result.items )
#set($replaceDeleteObject = $replaceDeleteObject + $separator + '{"Id" : { "S": "' + $item.Id + '" },"Sk" : { "S": "' + $item.Sk + '" }}')
#set($separator = ",")
#set($deleteObject = $replaceDeleteObject)
#end
$util.qr($ctx.stash.put("deleteObject", $deleteObject))
Later on I can access my deleteObject and it works properly.
My question however is, if it is possible to directly create some kind of JSON Object in vtl in which I can append my values instead of creating this string in the form of a JSON Object?
You can follow this example from the AppSync Batch docs:
#set($ids = [])
#foreach($id in ${ctx.args.ids})
#set($map = {})
$util.qr($map.put("id", $util.dynamodb.toString($id)))
$util.qr($ids.add($map))
#end
{
"version" : "2018-05-29",
"operation" : "BatchGetItem",
"tables" : {
"Posts": {
"keys": $util.toJson($ids),
"consistentRead": true
}
}
}
So for your case it should look like this:
#set ($batchDeleteArray = [])
#foreach( $item in $ctx.result.items )
#set ($entry = {
"Id": $util.dynamodb.toString($item.Id),
"Sk": $util.dynamodb.toString($item.Sk)
})
$util.qr($batchDeleteArray.add($entry))
#end
{
"version" : "2018-05-29",
"operation" : "BatchDeleteItem",
"tables" : {
"TableName": {
"keys": $util.toJson($batchDeleteArray)
}
}
}