I am beginner and as I understand @Transactional simply make sure that all the internal work of a class or method annotated with @Transactional will be wrapped in one transaction and all of the calls from external sources will create a new transaction but why do we actually need these annotations in Repository below and what are advantages of using it with readOnly = true in common cases? This is Spring pet-clinic example application using Spring & Hibernate (https://github.com/spring-projects/spring-petclinic).
/**
* Repository class for <code>Pet</code> domain objects All method names are compliant with Spring Data naming
* conventions so this interface can easily be extended for Spring Data See here: http://static.springsource.org/spring-data/jpa/docs/current/reference/html/jpa.repositories.html#jpa.query-methods.query-creation
*
* @author Ken Krebs
* @author Juergen Hoeller
* @author Sam Brannen
* @author Michael Isvy
*/
public interface PetRepository extends Repository<Pet, Integer> {
/**
* Retrieve all {@link PetType}s from the data store.
* @return a Collection of {@link PetType}s.
*/
@Query("SELECT ptype FROM PetType ptype ORDER BY ptype.name")
@Transactional(readOnly = true)
List<PetType> findPetTypes();
/**
* Retrieve a {@link Pet} from the data store by id.
* @param id the id to search for
* @return the {@link Pet} if found
*/
@Transactional(readOnly = true)
Pet findById(Integer id);
/**
* Save a {@link Pet} to the data store, either inserting or updating it.
* @param pet the {@link Pet} to save
*/
void save(Pet pet);
}