Dynamodb conditional update add or remove based on condition

Question

I have a dynamodb table in which one column is of type Map. I want an update query which removes the item from the map if the item is in the map or add the item to the map if the item is not in the map. How can i write a VTL fro this problem ?

Answer 1

You have to use a pipeline resolver for this.

I did this in a similar case for like/unlike with a single mutation .

You can change and adapt this code for your task.

likeEvent.req.vtl

#if( "$context.identity.username" =="guest")
   $util.unauthorized()
#end

#set($id=$util.autoId())
$util.qr($ctx.stash.put("sk", ".."))
$util.qr($ctx.stash.put("skBegining", ".."))
$util.qr($ctx.stash.put("id", ".."))
{}
likeEvent.res.vtl
{
    "value": "success"
}

checkIfLiked.req.vtl

{
  "version": "2018-05-29",
  "operation": "Query",
  "index": "creator-sk-index",
  "query" : {
           "expression": "creator = :creator  and begins_with(sk, :sk)  ",
           "expressionValues" : {
                ":creator" :  $util.dynamodb.toDynamoDBJson("$context.identity.username"),
                ":sk" :  $util.dynamodb.toDynamoDBJson("$ctx.stash.skBegining")
      }
  }
}

checkIfLiked.res.vtl

$util.toJson($ctx.result)

like.req.vtl

#if( "$context.stash.username" =="guest")
   $util.unauthorized()
#end
#set($sk=$ctx.stash.sk)
#set($id=$ctx.stash.id)
#set( $input = {} )
$util.qr($input.put("updatedAt", $util.time.nowEpochSeconds()))
$util.qr($input.put("createdAt", $util.time.nowEpochSeconds()))
$util.qr($input.put("creator", "$ctx.identity.username"))

#if($context.prev.result.items.size()!=0)
  {
      "version" : "2017-02-28",
      "operation" : "DeleteItem",
      "key" : {
          "id": $util.dynamodb.toDynamoDBJson("$context.prev.result.items[0].id"),
          "sk": $util.dynamodb.toDynamoDBJson("$context.prev.result.items[0].sk")
      }
  }
#else
  {
      "version" : "2017-02-28",
      "operation" : "PutItem",
      "key" : {
          "id": $util.dynamodb.toDynamoDBJson("$id"),
          "sk": $util.dynamodb.toDynamoDBJson("$sk")
      },
       "attributeValues" : $util.dynamodb.toMapValuesJson($input)

  }
#end

like.res.vtl

{
    "value": "success"
}