JPA Criteria api join through embedded ID

Question

I have the following entities:

@Entity
@Table(name = "place_revision")
public class PoiRevision {
    @OneToMany(mappedBy = "pk.revision", cascade = {CascadeType.ALL})
    private Collection<PoiRevisionCategory> categoryMapping;
    // ...
}

@Entity
@Table(name = "place_revision__category")
@AssociationOverrides({
    @AssociationOverride(name = "pk.revision",
        joinColumns = @JoinColumn(name = "place_revision_id")),
    @AssociationOverride(name = "pk.category",
        joinColumns = @JoinColumn(name = "category_id"))
})
public class PoiRevisionCategory {
    @EmbeddedId
    private PoiRevisionCategoryId pk = new PoiRevisionCategoryId();
    // ...
}

@Embeddable
public class PoiRevisionCategoryId implements Serializable {
    @ManyToOne
    private PoiRevision revision;
    @ManyToOne
    private Category category;
    // ...
}

@Entity
@Table(name = "category")
public class Category {
    @ManyToMany(targetEntity = Section.class, cascade = {CascadeType.PERSIST, CascadeType.MERGE}, fetch = FetchType.LAZY)
    @JoinTable(
        name = "category__section",
        joinColumns = @JoinColumn(name = "category_id"),
        inverseJoinColumns = @JoinColumn(name = "section_id")
    )
    private Collection<Section> sections;
    // ...
}

And want to select PoiRevisions that have Categories that have some Sections. I'm using Spring-data Specification to query the database for these entities.

My intent is to write something like:

Specification<PoiRevision> spec = new Specification<PoiRevision>() {
    @Override
    public Predicate toPredicate(Root<PoiRevision> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
        List<Predicate> conditions = new ArrayList<>(CONDITION_COUNT);

        CollectionJoin<PoiRevision, PoiRevisionCategory> mapping = root.join(PoiRevision_.categoryMapping);
        // BROKEN here as we cannot use nested path for joins
        Join<PoiRevisionCategory, Category> categories = mapping.join("pk.category"); 
        conditions.add(categories.get("sections").in(sections));

        // ...

        return cb.and(conditions.toArray(new Predicate[] {}));
    }
};

But we cannot use nested path for such joins as JPA provider (Hibernate, in my case) looks only for direct properties of PoiRevisionCategory class. And we cannot "join" embedded Id to our result set because it's not a manageable entity.

I'm really stuck with this issue which seems to be far from complicated when translated into SQL yet it has some complexity on the ORM-side.

Any idea is much appreciated.

Answer 1

After switching completely to metamodel API it became clearer and I was actually able to join embedded entity just like I tried and failed with string api.

So the correct way is just to join like one would normally do

Join<PoiRevisionCategory, PoiRevisionCategoryId> pk = mapping.join(PoiRevisionCategory_.pk);
Join<PoiRevisionCategoryId, Category> cats = pk.join(PoiRevisionCategoryId_.category);
CollectionJoin<Category, Section> sec = cats.join(Category_.sections);
conditions.add(sec.get(Section_.id).in(sections));

And it does the thing just fine!

What a relief.