Chapter 5: Managing Data Persistence with DynamoDB

1. Implement an update handler to update an existing movie item.

Answer: The handler expects a movie item in a JSON format; the input will be encoded to a Movie struct. The PutItem method is used to insert the movie to the table as follows:

func update(request events.APIGatewayProxyRequest) (events.APIGatewayProxyResponse, error) {
  var movie Movie
  err := json.Unmarshal([]byte(request.Body), &movie)
  if err != nil {
    return events.APIGatewayProxyResponse{
      StatusCode: 400,
      Body: "Invalid payload",
    }, nil
  }

  ...

  svc := dynamodb.New(cfg)
  req := svc.PutItemRequest(&dynamodb.PutItemInput{
    TableName: aws.String(os.Getenv("TABLE_NAME")),
    Item: map[string]dynamodb.AttributeValue{
      "ID": dynamodb.AttributeValue{
        S: aws.String(movie.ID),
      },
      "Name": dynamodb.AttributeValue{
        S: aws.String(movie.Name),
      },
    },
  })
  _, err = req.Send()
  if err != nil {
    return events.APIGatewayProxyResponse{
      StatusCode: http.StatusInternalServerError,
      Body: "Error while updating the movie",
    }, nil
  }

  response, err := json.Marshal(movie)
  ...

  return events.APIGatewayProxyResponse{
    StatusCode: 200,
    Body: string(response),
    Headers: map[string]string{
      "Content-Type": "application/json",
    },
  }, nil
}

2. Create a new PUT method in API Gateway to trigger the update Lambda function.

Answer: Expose a PUT method on the /movies resource and configure the target to be the Lambda function defined earlier. The following screenshot illustrates the results:

 

3. Implement a single Lambda function to handle all type of events (GET, POST, DELETE, PUT).Answer:

func handler(request events.APIGatewayProxyRequest) (events.APIGatewayProxyResponse, error) {
 switch request.HTTPMethod {
 case http.MethodGet:
 // get all movies handler
 break
 case http.MethodPost:
 // insert movie handler
 break
 case http.MethodDelete:
 // delete movie handler
 break
 case http.MethodPut:
 // update movie handler
 break
 default:
 return events.APIGatewayProxyResponse{
 StatusCode: http.StatusMethodNotAllowed,
 Body: "Unsupported HTTP method",
 }, nil
 }
}

4. Update the findOne handler to return a proper response code for a valid request but an empty data (for example, no movie for the ID requested).

Answer: When handling input of a user (movie ID in our case), validation is mandatory. Hence, you need to write a regular expression to ensure the ID given in parameter is properly formed. The following are examples of regular expressions to validate an ID:

• • Pattern for alphanumeric ID: [a-zA-Z0-9]+
  • Pattern for digits only ID: [0-9]+

5. Implement a pagination system on the findAll endpoint using a Range header and using a Query string.

Answer: Use the Limit option in the ScanRequest method to limit number of returned items:

dynamodbClient := dynamodb.New(cfg)
req := dynamodbClient.ScanRequest(&dynamodb.ScanInput{
    TableName: aws.String(os.Getenv("TABLE_NAME")),
    Limit: aws.Int64(int64(size)),
})

The number of items to return can be read from the request headers:

size, err := strconv.Atoi(request.Headers["Size"])