Lottery System

The system should have a way to create Lotteries. Users can participate in any lottery that isn't finished yet. When you participate to a Lottery you become part of its extraction pool of potential winners. Once the Lottery closes a random winner is extracted from the pool and save winner number in a storage.

Logic is:

• The service will allow anyone to register as a lottery participant.
• Lottery participants will be able to submit as many lottery ballots for any lottery that isn’t yet finished.
• Each day at midnight the lottery event will be considered closed and a random lottery winner will be selected from all participants for the day.
• All users will be able to check the winning ballot for any specific date.
• The service will have to persist the data regarding the lottery.

Additionally:

• An unregistered user cannot purchase lottery tickets.
• The lottery can always be started with the lottery name. The only rule is that multiple active lotteries cannot be created with the same lottery name.
• The lottery ticket number has a unique sequential generated number per lottery starting at 1.

1 - How to Run Project

• Running with Docker Compose

Simply use:

$ docker-compose up
$ docker-compose down

• Running on Your Local

Prerequisites

• Java 11
• Postgresql
• Your preferred IDE
  • Eclipse
  • IntelliJ IDEA
  • VS Code

Create your database named lottery in postgresql and change application.properties as :

spring.datasource.url=jdbc:postgresql://localhost:5432/lottery
spring.datasource.username=postgres
spring.datasource.password=password

## Hibernate Properties
# The SQL dialect makes Hibernate generate better SQL for the chosen database
spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.PostgreSQLDialect

# Hibernate ddl auto (create, create-drop, validate, update)
spring.jpa.hibernate.ddl-auto = create
spring.jpa.generate-ddl=true
spring.jpa.show-sql=true

spring.mvc.view.prefix: /
spring.mvc.view.suffix: .jsp
spring.messages.basename=validation

Then run that command in terminal:

$ mvn clean spring-boot:run

2 - Tools and Technologies Used

• Spring Boot- 2.0.4.RELEASE
• JDK - 1.8 or later
• Spring Framework - 5.0.8 RELEASE
• Hibernate - 5.2.17.Final
• Spring Data JPA
• Maven - 3.2+
• IDE - IntelliJ IDEA
• PostgreSQL - 42.2.5
• JSP
• Spring Security
• Spring Web
• Postman
• SonarLint

3 - Packaging Structure

Following is the packing structure of our Lottery System:

4 - Database Design

Since I am planning on querying the database with different queries and I need to join between storages I prefered using a standard SQL database and not a NoSQL approach. NoSQL databases really shine if the data to store is not so well defined. However, I have a clear pattern of data to store.

I have 4 tables for the lottery design. One called lottery which holds the lottery information for the current lottery and one called lottery_ticket holding the ticket information for the lotteries. Users table holds user details and role table defines user role. Here is how I design:

lottery

• id
• name
• start_date
• end_date
• winner_lottery_num

lottery_ticket

• id
• lottery_id
• username
• lottery_number (The number of the ticket in the current lottery. It contains sequential numbers per lottery.)
• date

users

• id
• username
• first_name
• last_name
• password
• role

role

• id
• name

The PostgreSQL database looks like:

5 - Exception(Error) Handling for RESTful Services

Spring Boot provides a good default implementation for exception handling for RESTful Services. @ControllerAdvice is a specialization of the @Component annotation which allows to handle exceptions across the whole application in one global handling component.

• Resource Not Present

Here's what happens when you fire a request to a resource not found:

http://localhost:8080/lottery/endLotteryAndSelectRandomLotteryWinner/5

{  
   "timestamp": "2020-12-23T16:44:39.079+00:00",  
   "message": "Lottery not found for this id :: 5",  
   "details": "uri=/lottery/endLotteryAndSelectRandomLotteryWinner/5"  
}  

• Get Active Lottery Result

http://localhost:8080/lottery/lotteryResult/5

{  
   "timestamp": "2020-12-23T17:16:46.879+00:00",  
   "message": "Lottery is not finish yet :: 5",  
   "details": "uri=/lotteryResult/5"  
}  

• Invalid User Registration

http://localhost:8080/register

{  
   "timestamp": "2020-12-23T14:13:02.501+00:00",  
   "message": "user already exist :: mervekay",  
   "details": "uri=/register"  
}  

6 - Testing REST APIs via Postman Client

You can find all api queries in the attachted postman collection here.

• User registration

• Throws exception if user trys to register with same username

• Get all active lotteries

• Submit lottery ticket

• Throws exception if user trys to submit ticket with unregistered username

• Throws exception if user trys to submit ticket for passive lottery

• End lottery by lottery id

• Throws exception if lottery does not exist

7 - Coulda/Woulda/Shoulda

• I would have implemented integration tests.
• I could have loaded data from the xml file using the dbunit library while writing unit tests.
• I would have completed front-end part.
• I could have extended queries usign DateUtils.
• I could have implemented submit ticket endpoint without username parameter, I could have get active user automatically.
• I would have dockerized the project.
• I could have designed the project for a distributed system. I lock the submitLotteryTicket method and let only one thread can run the endpoint at a time. Since each lottery number is generated sequentially, I need to be sure each user has a unique lottery number per lottery. A better solution would be generating a sequence numbers for a distributed system.