How to execute a Join query in Hibernate/Spring Data?

Question

Java

What if the information I want to show lies in several tables? How to make a join request in Hibernate or for example Spring Data Jpa? I found an example of this code:

EntityManager em = emf.createEntityManager();
em.getTransaction().begin();
  
List<Object[]> results = em.createQuery("SELECT p.firstName, p.lastName, n.phoneNumber FROM Person p, PhoneBookEntry n WHERE p.firstName = n.firstName AND p.lastName = n.lastName").getResultList();

for (Object[] result : results) {
  log.info(result[0] + " " + result[1] + " - " + result[2]);
}

em.getTransaction().commit();
em.close();

A list of Object arrays and getting by index looks strange to say the least :) What other options are there? I read about DTO, it looks logical, but the question arises: if the application consists of a bunch of entities, will there be a lot of DTO too?

Answer 1

What you need is called projection https://www.baeldung.com/spring-data-jpa-projections
And, in general, yes - how many requests with different data will be, so many DTOs will need to be created - the repository you need to know what type of object to build.
Or, yes, List, since there is no other option to return untyped data.