Spring data JPA Specifications - #OneToMany dependency - spring

Question

i have a problem with getting List from entity Person using Spring data JPA specifications (because of pagination). I need to get all notes by person but dependency between these two entities is on Person side. I don't know how to create my Predicate because Note doesn't contain any attribute related to Person.
I simply can get List with Persons getter but i can't use this way because i need returned data paginated.
#Entity
public class Person implements Serializable {
#Id
private Long personId;
#OneToMany
#JoinColumn(name = "personId")
private List<Note> notes;
}
#Entity
public class Note implements Serializable {
#Id
private Long noteId;
}
Normally, I would write something like this, but i don't have an attribute person in Note and database can't be remapped at this stage.
public static Specification<Note> notesByPerson(final Long personId) {
return new Specification<Note>() {
#Override
public Predicate toPredicate(final Root<Note> root, final CriteriaQuery<?> query,
final CriteriaBuilder builder) {
final Path<Person> per = root.<Person> get("person");
return builder.equal(per.<Long> get("personId"), personId);
}
};
}
Thank you,
Zdend

Answer 1

Solved..
public static Specification<Note> notesByPerson(final Long personId) {
return new Specification<Note>() {
#Override
public Predicate toPredicate(final Root<Note> noteRoot, final CriteriaQuery<?> query,
final CriteriaBuilder cb) {
final Subquery<Long> personQuery = query.subquery(Long.class);
final Root<Person> person = personQuery.from(Person.class);
final Join<Person, Note> notes = person.join("notes");
personQuery.select(notes.<Long> get("noteId"));
personQuery.where(cb.equal(person.<Long> get("personId"), personId));
return cb.in(noteRoot.get("noteId")).value(personQuery);
}
};
}

Answer 2

I am not sure how to do that with Predicates, as I usually dont use them, but in JPQL (or HQL, which is similar), you can do something like this:
SELECT Note n FROM Person.notes WHERE XXXX
It is basically the same thing as doing this in SQL
SELECT n.noteId FROM person as p JOIN persons_notes pn ON pn.person=p.personId JOIN notes as n ON n.noteId=pn.noteId
I would venture a guess that the Predicate method has similar abilities as described above.