AWS AppSync - Create Mutation returns Null - amazon-web-services

Question

I've got a simple AppSync API that has a type for City and Venue, the example is to map small retail shops. I'm trying to create a new City via the "Queries" pane within AppSync, I'm also wanting to provide a shortened ID - as opposed to the long autoId so that I can run queries for the shortened ID and the frontend app can use it from the params in the URL.
I'm trying to create a new item in DynamoDB with the following code:
Schema
type City {
id: String!
name: String!
}
type Mutation {
...
createCity(input: CreateCityInput!): City
...
}
input CreateCityInput {
id: String!
name: String!
}
Mutation.createCity
// Request mapping template
{
"version" : "2017-02-28",
"operation" : "PutItem",
"key" : {
## If object "id" should come from GraphQL arguments, change to $util.dynamodb.toDynamoDBJson($ctx.args.id)
"id": $util.dynamodb.toDynamoDBJson($ctx.args.id)
},
"attributeValues" : $util.dynamodb.toMapValuesJson($ctx.args)
}
// Response mapping template
$util.toJson($context.result)
Here's the mutation that I ran within the Queries page
mutation CreateCity {
createCity(input: {
id: "11538062"
name: "Manchester"
}) {
id
name
}
}
And this is the error that is returned from AppSync and or Dynamo
{
"data": {
"createCity": null
},
"errors": [
{
"path": [
"createCity"
],
"data": null,
"errorType": "DynamoDB:AmazonDynamoDBException",
"errorInfo": null,
"locations": [
{
"line": 32,
"column": 3,
"sourceName": null
}
],
"message": "One or more parameter values were invalid: Type mismatch for key id expected: S actual: NULL (Service: AmazonDynamoDBv2; Status Code: 400; Error Code: ValidationException; Request ID: 7PU4D2...)"
}
]
}
Any help would be really appreciated, I can't see why I'm unable to perform a simple Create using a provided String as the ID and it identifies it as NULL...

Answer 1

## Request Mapping
{
"version" : "2017-02-28",
"operation" : "PutItem",
"key" : {
"id" : $util.dynamodb.toDynamoDBJson($ctx.args.input.id)
},
"attributeValues" : {
"name" : $util.dynamodb.toDynamoDBJson($ctx.args.input.name)
}
}