| name | spring-data-jpa-skill |
| description | Implement the persistence layer using Spring Data JPA in Spring Boot applications. |
Follow the below principles when using Spring Data JPA:
-
Disable the Open Session in View (OSIV) filter:
spring.jpa.open-in-view=false
-
Disable in-memory pagination:
spring.jpa.properties.hibernate.query.fail_on_pagination_over_collection_fetch=true
-
Avoid the N+1 SELECT problem: use JOIN FETCH to load associated child collections in a single query.
-
Avoid in-memory pagination: when loading a paginated list of parent entities with child collections:
- First, load only the parent IDs using pagination
- Then, load the full entities with their child collections using JOIN FETCH for those IDs
- Assemble the final Page from the paginated IDs and the loaded entities
Pagination with child collections example:
PostRepository.java
public interface PostRepository extends JpaRepository<Post, Long> {
@Query("select p.id from Post p order by p.id")
Page findPostIds(Pageable pageable);
@Query("select distinct p from Post p left join fetch p.comments where p.id in :ids")
List findAllByIdInWithComments(@Param("ids") Collection ids);
}
PostService.java
@Service
public class PostService {
private final PostRepository postRepository;
public PostService(PostRepository postRepository) {
this.postRepository = postRepository;
}
@Transactional(readOnly = true)
public Page findPosts(Pageable pageable) {
Page idsPage = postRepository.findPostIds(pageable);
if (idsPage.isEmpty()) {
return Page.empty(pageable);
}
List posts = postRepository.findAllByIdInWithComments(idsPage.getContent());
return new PageImpl<>(posts, pageable, idsPage.getTotalElements());
}
}
