Spring JPA one to many join - spring

Question

#Entity
#Getter #Setter
public class IndieApp {
#Id
#Column(name = "indie_app_id")
private Long id;
#Column(name = "name")
private String name;
#OneToMany(mappedBy = "indieApp")
private List<Genre> genres = new ArrayList<>();
}
#Entity
#Getter #Setter
public class Genre {
#Id
#Column(name = "genre_id")
private Long genreId;
#Column(name = "description")
private String description; //like "RPG", "Action"
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "indie_app_id")
private IndieApp indieApp;
}
#Data
public class RandomRecDto {
private final Long id;
private final String name;
private final String genres;
}
#Repository
#RequiredArgsConstructor
public class RandomRecRepository {
private final EntityManager em;
public List<RandomRecDto> findRandomApps() {
return em.createQuery(
"select new study.weba.studyJPA.dto.RandomRecDto(i.id, i.name, g.description)" +
" from IndieApp i join i.genres g", RandomRecDto.class)
.setMaxResults(12)
.getResultList();
}
}
Hello seniors!
When i put the dummy data as shown below,
indie_app_id
name
1
App1
2
App2
genre_id
description
indie_app_id
1
Action
1
2
RPG
1
3
FPS
2
4
Sport
2
i can get result like this.
randomRecDto = RandomRecDto(id=1, name=App1, genres=Action)
randomRecDto = RandomRecDto(id=1, name=App1, genres=RPG)
randomRecDto = RandomRecDto(id=2, name=App2, genres=FPS)
randomRecDto = RandomRecDto(id=2, name=App2, genres=Sport)
However, result that i want is like this.
randomRecDto = RandomRecDto(id=1, name=App1, genres=Action, RPG)
randomRecDto = RandomRecDto(id=2, name=App2, genres=FPS, Sport)
I want to get description by array.
What should I do?

Answer 1

Why don't you get IndieApp entities and then convert them into your RandomRecDto DTO? This would even simplify your Repository that would handle IndieApp instead of RandomRecDto:
public interface IndieAppRepository extends JpaRepository<IndieApp, Long> {
List<IndieApp> findTop12();
}
You may want to read more details about Spring Data in the following links:
Spring Data JPA
Spring Data Repositories
Limiting query results with Spring Data JPA
Defining Spring Data Query Methods
Spring Data Repositories Query Keywords

Answer 2

JpaResultMapper jpaResultMapper = new JpaResultMapper();
String sql = "SELECT i.indie_app_id, i.name, group_concat(g.description separator ',') FROM indie_app AS i" +
" JOIN genre AS g ON i.indie_app_id = g.indie_app_id" +
" group by i.indie_app_id, i.name";
Query nativeQuery = em.createNativeQuery(sql);
List<RandomRecDto> results = jpaResultMapper.list(nativeQuery, RandomRecDto.class);