Why hibernate entity graph fetch nested lazy collections - spring

Question

I am trying to use entity graph for triggering lazy collections to load but unfortunately entity graph also triggers all nested collections. I am using spring-data-jpa-entity-graph library for creating entity graphs at runtime.
#Entity
public class Brand implements Serializable {
#OneToMany(mappedBy = "brand", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
private Set<Vehicle> vehicles;
}
#Entity
public class Vehicle implements Serializable {
#ManyToOne
#JoinColumn(name = "brand_id")
private Brand brand;
#OneToMany(mappedBy = "vehicle", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
private Set<VehiclePart> parts;
}
#Entity
public class VehiclePart implements Serializable {
#ManyToOne
#JoinColumn(name = "vehicle_id")
private Vehicle vehicle;
}
Spring service with JPA repository:
public interface BrandsRepository extends EntityGraphJpaRepository<Brand, Long> {
Page<Brand> findAll(Pagable pagable, EntityGraph entityGraph);
}
#Service
public class BrandsService {
public List<Brand> find() {
return repository.findAll(PageRequest.of(0, 10, Sort.by(Sort.Direction.ASC, "id")), EntityGraphUtils.fromAttributePaths("vehicles")).getContent();
}
}
In this case service also return parts collection for each vehicle but I would like to fetch only list of brands with vehicles collection for each brand.
How can we trigger to load lazy collections just on the first level (only brand's vehicles -- without vehicle's parts)?

Answer 1

I had the same problem. In my case: Spring and hibernate acted correctly, but I can see, that unused (lazy) fields are queried from sql.
When you use the fields, then they will be loaded over sql.
Iam using lombok and #EqualsAndHashCode.Exclude and #ToString.Exclude helps to prevent that.
In your case: Add a DTO-layer. Do not return the entities themself.
Or use #JsonIgnore annotation to ignore fields.