create-function-point.ts

//-----------------------------------------------------------------------------------------------------------------------
/* 
 * Create a lambda function handler for a graphQL typeName.fieldName 
 */
//-----------------------------------------------------------------------------------------------------------------------
const createAppSyncLambdaHandler = function (stack: cdk.Stack, api: appsync.GraphQLApi, recipe: {
  name: string,                               // XXX autogenerate frome type.field the name root of the name for the handler and data source
  environment: { [key: string]: string },     // @see https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-lambda.Function.html
  permissions: { obj: any, func: any },       // the currently singleton permissions for the handler to e.g. talk to dynamoDB
  description: string,                        // text description attached to various created objects (can be undefined)
  typeName: string,                           // the GraphQL name of the type that will be handled
  fieldName: string,                          // the name of the field in the type that will be handled
  respTemplate?: string                       // response template if the default won't work (might evolve to 'set vs singleton' as those are the main types)
  timeout?: cdk.Duration                      // optional timeout
  memorySize?: number                         // optional memory size
}): lambda.Function {                         // return function so can be referenced elsewhere e.g. for CFT Outputs

  if (!recipe.memorySize) {
    recipe.memorySize = 512;  // default set to knee of perf curve for many examples found on web
  }
  const handler = new lambda.Function(stack, recipe.name, {
    runtime: lambda.Runtime.NODEJS_12_X,
    code: lambda.Code.fromInline(defaultLambdaCode),
    handler: 'index.handler',
    environment: recipe.environment,
    timeout: recipe.timeout,
    logRetention: 7,
    memorySize: recipe.memorySize,
  });

  // XXX permissions an array
  recipe.permissions.func.apply(recipe.permissions.obj, [handler]);

  const dataSource = api.addLambdaDataSource(
    recipe.name + 'DataSource',
    recipe.description,
    handler,
  );

  dataSource.createResolver({
    typeName: recipe.typeName,
    fieldName: recipe.fieldName,
    requestMappingTemplate: appsync.MappingTemplate.lambdaRequest(`
        {
            "subscriber": $util.dynamodb.toDynamoDBJson($ctx.identity.sub),
            "context": $utils.toJson($context.arguments)
        }
      `),
    responseMappingTemplate: appsync.MappingTemplate.fromString( `$util.toJson($ctx.result)`),
  });

  return handler;
}

usage.ts

    const setUserMfgrApiTokenHandler = createAppSyncLambdaHandler(this, api, {
      typeName: 'Mutation',
      fieldName: 'setUserMfgrApiToken',
      description: 'Lambda resolver for setUserMfgrApiToken',
      name: 'setUserMfgrApiTokenHandler',
      environment: {
        userDevicesTable: userTable.tableName,
        firstTimeQueue: firstTimeQueue.queueUrl,
      },
      permissions: { obj: userTable, func: userTable.grantReadWriteData },
    });