Creating an AWS AppSync GraphQL API with CDK

cdk-chat-stack.ts

const api = new GraphqlApi(this, 'cdk-chat-app-api', {
  name: "cdk-chat-app",
  logConfig: {
    fieldLogLevel: FieldLogLevel.ALL,
  },
  schema: Schema.fromAsset('graphql/schema.graphql'),
  authorizationConfig: {
    defaultAuthorization: {
      authorizationType: AuthorizationType.USER_POOL,
      userPoolConfig: {
        userPool
      }
    },
  },
});

new cdk.CfnOutput(this, "GraphQLAPIURL", {
  value: api.graphqlUrl
});

// Configure the two tables
const messageTableDs = api.addDynamoDbDataSource('Message', messageTable);
const roomTableDs = api.addDynamoDbDataSource('Room', roomTable);

// Create the resolvers
messageTableDs.createResolver({
  typeName: 'Query',
  fieldName: 'listMessagesForRoom',
  requestMappingTemplate: MappingTemplate.fromString(`
  {
    "version" : "2017-02-28",
    "operation" : "Query",
    "index" : "messages-by-room-id",
    "query" : {
      "expression": "roomId = :roomId",
      "expressionValues" : {
        ":roomId" : $util.dynamodb.toDynamoDBJson($context.arguments.roomId)
      }
      
    }
    #if( !$util.isNull($ctx.arguments.sortDirection)
          && $ctx.arguments.sortDirection == "DESC" )
      ,"scanIndexForward": false
    #else
      ,"scanIndexForward": true
    #end
    #if($context.arguments.nextToken)
      ,"nextToken": "$context.arguments.nextToken"
    #end
}
  `),
  responseMappingTemplate: MappingTemplate.fromString(`
    #if( $ctx.error )
      $util.error($ctx.error.message, $ctx.error.type)
    #else
      $util.toJson($ctx.result)
    #end`
  )
})

messageTableDs.createResolver({
  typeName: 'Mutation',
  fieldName: 'createMessage',
  requestMappingTemplate: MappingTemplate.fromString(`
  ## Automatically set the id if it's not passed in.
  $util.qr($context.args.input.put("id", $util.defaultIfNull($ctx.args.input.id, $util.autoId())))
  ## Automatically set the createdAt timestamp.
  #set( $createdAt = $util.time.nowISO8601() )
  $util.qr($context.args.input.put("createdAt", $util.defaultIfNull($ctx.args.input.createdAt, $createdAt)))

  ## Automatically set the user's username on owner field.
  $util.qr($ctx.args.input.put("owner", $context.identity.username))

  ## Create a condition that will error if the id already exists
  #set( $condition = {
    "expression": "attribute_not_exists(#id)",
    "expressionNames": {
        "#id": "id"
    }
  } )

  {
    "version": "2018-05-29",
    "operation": "PutItem",
    "key": {
      "id":   $util.dynamodb.toDynamoDBJson($ctx.args.input.id)
    },
    "attributeValues": $util.dynamodb.toMapValuesJson($context.args.input),
    "condition": $util.toJson($condition)
  }
  `),
  responseMappingTemplate: MappingTemplate.dynamoDbResultItem()
})

roomTableDs.createResolver({
  typeName: 'Query',
  fieldName: 'listRooms',
  requestMappingTemplate: MappingTemplate.fromString(`
    #set( $limit = $util.defaultIfNull($context.args.limit, 1000) )
    #set( $ListRequest = {
      "version": "2018-05-29",
      "limit": $limit
    } )
    #if( $context.args.nextToken )
      #set( $ListRequest.nextToken = $context.args.nextToken )
    #end
    $util.qr($ListRequest.put("operation", "Scan"))
    $util.toJson($ListRequest)
  `),
  responseMappingTemplate: MappingTemplate.fromString(`
    #if( $ctx.error)
      $util.error($ctx.error.message, $ctx.error.type)
    #else
      $util.toJson($ctx.result)
    #end
  `)
})

roomTableDs.createResolver({
  typeName: 'Mutation',
  fieldName: 'createRoom',
  requestMappingTemplate: MappingTemplate.fromString(`
  $util.qr($context.args.input.put("id", $util.defaultIfNull($ctx.args.input.id, $util.autoId())))
  {
    "version": "2018-05-29",
    "operation": "PutItem",
    "key": {
      "id":   $util.dynamodb.toDynamoDBJson($ctx.args.input.id)
    },
    "attributeValues": $util.dynamodb.toMapValuesJson($context.args.input),
    "condition": $util.toJson($condition)
  }
  `),
  responseMappingTemplate: MappingTemplate.dynamoDbResultItem() 
})