05-1-B-Spring-CRUD-and-Service.adoc

CRUD Repositories and Services

Previously, in the ca.mcgill.ecse321.eventregistration.dao.EventRegistrationRepository class we used an instance of javax.persistence.EntityManager from Hibernate to directly to implement the required operations related to saving/retrieving data to/from a database (Create, Read, Update, and Delete operations, shortly, CRUD). This section will introduce the Spring framework’s inbuilt support for such CRUD operations via the org.springframework.data.repository.CrudRepository interface and will show how to use such repositories to implement your use cases in so-called service classes.

If you would like to, you can obtain a version of the project that already has the changes from the previous tutorials here.

Creating a CRUD Repository

1. Create a new interface PersonRepository in the ca.mcgill.ecse321.eventregistration.dao package and extend the CrudRepository<Person, String> interface

2. Create a new method Person findByName(String name)

   package ca.mcgill.ecse321.eventregistration.dao;
   
   import org.springframework.data.repository.CrudRepository;
   
   import ca.mcgill.ecse321.eventregistration.model.Person;
   
   public interface PersonRepository extends CrudRepository<Person, String>{
   
   	Person findPersonByName(String name);
   
   }

3. Since Spring supports automated JPA Query creation from method names (see possible language constructs here) we don’t need to implement the interface manually, Spring JPA will create the corresponding queries runtime! This way we don’t need to write SQL queries either.

4. Create interfaces for the Event and Registration classes as well
   EventRepository.java:

   package ca.mcgill.ecse321.eventregistration.dao;
   
   import org.springframework.data.repository.CrudRepository;
   
   import ca.mcgill.ecse321.eventregistration.model.Event;
   
   public interface EventRepository extends CrudRepository<Event, String> {
   
   	Event findEventByName(String name);
   
   }

   RegistrationRepository.java:

   package ca.mcgill.ecse321.eventregistration.dao;
   
   import java.util.List;
   
   import org.springframework.data.repository.CrudRepository;
   
   import ca.mcgill.ecse321.eventregistration.model.Event;
   import ca.mcgill.ecse321.eventregistration.model.Person;
   import ca.mcgill.ecse321.eventregistration.model.Registration;
   
   public interface RegistrationRepository extends CrudRepository<Registration, Integer> {
   
   	List<Registration> findByPerson(Person personName);
   
   	boolean existsByPersonAndEvent(Person person, Event eventName);
   
   	Registration findByPersonAndEvent(Person person, Event eventName);
   
   }

Implementing Services

We implement use-cases in service classes by using the CRUD repository objects for each data type of the domain model.

1. In src/main/java, create a new package ca.mcgill.ecse321.eventregistration.service.

2. In this package, create the EventRegistrationService class as shown below

   package ca.mcgill.ecse321.eventregistration.service;
   
   import java.sql.Date;
   import java.sql.Time;
   import java.util.ArrayList;
   import java.util.List;
   
   import org.springframework.beans.factory.annotation.Autowired;
   import org.springframework.stereotype.Service;
   import org.springframework.transaction.annotation.Transactional;
   
   import ca.mcgill.ecse321.eventregistration.dao.EventRepository;
   import ca.mcgill.ecse321.eventregistration.dao.PersonRepository;
   import ca.mcgill.ecse321.eventregistration.dao.RegistrationRepository;
   import ca.mcgill.ecse321.eventregistration.model.Event;
   import ca.mcgill.ecse321.eventregistration.model.Person;
   import ca.mcgill.ecse321.eventregistration.model.Registration;
   
   @Service
   public class EventRegistrationService {
   
   	@Autowired
   	EventRepository eventRepository;
   	@Autowired
   	PersonRepository personRepository;
   	@Autowired
   	RegistrationRepository registrationRepository;
   
   	@Transactional
   	public Person createPerson(String name) {
   		Person person = new Person();
   		person.setName(name);
   		personRepository.save(person);
   		return person;
   	}
   
   	@Transactional
   	public Person getPerson(String name) {
   		Person person = personRepository.findPersonByName(name);
   		return person;
   	}
   
   	@Transactional
   	public List<Person> getAllPersons() {
   		return toList(personRepository.findAll());
   	}
   
   	@Transactional
   	public Event createEvent(String name, Date date, Time startTime, Time endTime) {
   		Event event = new Event();
   		event.setName(name);
   		event.setDate(date);
   		event.setStartTime(startTime);
   		event.setEndTime(endTime);
   		eventRepository.save(event);
   		return event;
   	}
   
   	@Transactional
   	public Event getEvent(String name) {
   		Event event = eventRepository.findEventByName(name);
   		return event;
   	}
   
   	@Transactional
   	public List<Event> getAllEvents() {
   		return toList(eventRepository.findAll());
   	}
   
   	@Transactional
   	public Registration register(Person person, Event event) {
   		Registration registration = new Registration();
   		registration.setId(person.getName().hashCode() * event.getName().hashCode());
   		registration.setPerson(person);
   		registration.setEvent(event);
   
   		registrationRepository.save(registration);
   
   		return registration;
   	}
   
   	@Transactional
   	public List<Registration> getAllRegistrations(){
   		return toList(registrationRepository.findAll());
   	}
   
   	@Transactional
   	public List<Event> getEventsAttendedByPerson(Person person) {
   		List<Event> eventsAttendedByPerson = new ArrayList<>();
   		for (Registration r : registrationRepository.findByPerson(person)) {
   			eventsAttendedByPerson.add(r.getEvent());
   		}
   		return eventsAttendedByPerson;
   	}
   
   	private <T> List<T> toList(Iterable<T> iterable){
   		List<T> resultList = new ArrayList<T>();
   		for (T t : iterable) {
   			resultList.add(t);
   		}
   		return resultList;
   	}
   
   }