Join 3 tables in Spring Jpa Data - spring

Question

I've been struggling lately to join 3 tables with spring data jpa. I have 3 entities, Series, Dossier and Item. Series has many Dossiers, and Dossier has many Items (Relationships). I do something like Series.join(Dossier_.series).join(Dossier_.items) and I end up with a Join set. I want to make the following query:
Select Items from Series,Dossier,Item
Where Series.Id=Dossier.seriesId
and Dossier.id=Item.dossierId
and series.projectId = :param
I can't express this statement with Spring Specifications and criteria api....Please shed some light

Answer 1

It is more a JPA question.
First, I always emphasize, you are not access "tables". You should view them as domain entities. Lot of misuse of JPA/Hibernate/other ORMs actually comes from direct "translate" of SQL or database concepts.
Back to your question, the answer is simple. First make sure you actually have the "relationships" in your domain entities. Storing IDs is not helping to build a concrete domain model. For example, you have something like :
#Entity
class Series {
#Id
Long id;
#OneToMany(mappedBy="series")
List<Dossier> dossiers;
}
#Entity
class Dossier{
#Id
Long id;
#ManyToOne
Series series;
#OneToMany(mappedBy="dossier"
List<Item> items;
}
#Entity
class Item{
#Id
Long id;
#ManyToOne
Dossier dossier;
}
The query is straight-forward:
select s.dossiers.items from Series s where s.projectId = :param
Or, if it is more reasonable to have only the #ManyToOnes and omit the #OneToManys, the query is still straight-forward:
from Item where i.dossier.series.projectId = :param

Answer 2

[Still rocky here] Maybe i didn't make myself clear.I know how to express the query in HQL.The problem is to use Spring Data's Specifications,with the help of the criteria api to build that query.
//Let's exampine the following piece of code
public class CustomItemSpecs {
public static Specification<Item> createSpecificationFromSearchForm(final SearchForm searchForm) {
return new Specification<Item>() {
#Override
public Predicate toPredicate(Root<Item> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
CriteriaQuery<Item> cq = cb.createQuery(Item.class);
CriteriaQuery<Series> sb = cb.createQuery(Series.class);
Root<Series> series = sb.from(Series.class);
Join<Series,Dossier> join1 = series.join(Series_.dossiers);
Join<Dossier, Item> join2 = join1.join(Dossier_.items);
}
}
}
As you can see i manage to do two seperate joins.The problem is when i want to join Series,Dossier And Items to execute the above query.Notice that join2 is a Dossier-Item set.I can't make criteria like cb.equals(join2.get(Series_.projectId),)

Answer 3

im using spring data interface projection .
example like this
note items must be interface class
Repository Class
#Repository
public interface ItemRepository extends JpaRepository<Items,Long> {
#Query(nativeQuery = true,value = "Select Items from Series,Dossier,Item Where Series.Id=Dossier.seriesId and Dossier.id=Item.dossierId and series.projectId = :param")
public Items findTransaksisByAccountIdOrderById(#Param("param") Long projectId);
}