Get children for any level in tree structure but without theirs children using Hibernate? - mysql

Question

I have a Folder entity in Hibernate, like so:
#Entity
#Table(name = "folders")
public class Folder {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "folder_id", unique = true, nullable = false)
private int id;
#NonNull
#Column(name = "name", length = 100, unique = true, nullable = false)
private String name;
#OneToMany(fetch = FetchType.EAGER, mappedBy = "parent", orphanRemoval = true)
#Column(name = "sub_folders")
private Set<Folder> childFolders = new HashSet<>();
#ManyToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
#JsonIgnore
#JoinColumn(name = "parent", referencedColumnName = "folder_id", nullable = true)
private Folder parent;
public Folder() {
}
}
I'm trying to write a finder method or custom query which will do what I wrote in the subject.
So if I send a request going like folders/{parent_folder_id}, let's say value being 1, I should get objects 4 and 5, but without their children, so not including 6,7,8 and 9.
Ideally, hibernate query would be preferred. If not, any sql language is also fine. I'll try to tumble it up to hibernate.
This is what I got, I still get children...
#Query(value = "Select * from folders f where f.parent = ?1 ", nativeQuery = true)
Set<Folder> getFolders(int folder_id);

Answer 1

I think this should work:
make the default fetchtype lazy:
#OneToMany(fetch = FetchType.EAGER, mappedBy = "parent", orphanRemoval = true)
#Column(name = "sub_folders")
private Set<Folder> childFolders = new HashSet<>();
Use a JOIN FETCH in order to eagerly fetch the relationships you want.
SELECT f FROM folders f JOIN FETCH f.childFolders
You probably can achieve something similar with entity graphs but I'm not sure about their interaction with queries.

Answer 2

I got what I need with following query:
#Query(value = "Select folder_id, name, parent From folders f Where f.parent = ?1", nativeQuery = true)
This will give me just name of the folder and its Id.