Add Query Hint inside of JPA Specification

Question

I'm looking for a way to add a QueryHint inside of a Specifications toPredicate method. As I'm only having access to Root<T>, CriteriaQuery<?> and CriteriaBuilder instances I'm wondering if this is even possible.

I'm also okay with setting a global default, so that the hint is applied to all queries globally, but I would prefer to somewhat add it inside of the Specification. Maybe hibernate has a property I didn't spot in it's hibernate.properties file to achieve that.

I know I could achieve that by overriding the JpaSpecificationExecutors corresponding method and annotate the method with @QueryHints, but as I would have to do that for all Repositories, I would prefer to not do that as it is somewhat error prone.

Thanks in advance.

Answer 1

It's possible but you have to apply Criteria API directly without Spring Data wrappers. Here is an example from Vlad Mihalcea's article.

CriteriaBuilder builder = entityManager.getCriteriaBuilder();
 
CriteriaQuery<Post> criteria = builder.createQuery(Post.class);
Root<Post> fromPost = criteria.from(Post.class);
 
criteria.where(
    builder.in(
        fromPost.get("id")).value(Arrays.asList(1, 2, 3)
    )
);
 
List<Post> posts = entityManager
    .createQuery(criteria)
    .setHint("hint_name", "hint_value")
    .getResultList();

If you do want to stick to Spring Data Specification, you can try to use @QueryHints annotation.

public interface RobotRepositoryRobot extends JpaRepository<Robot, Long>, JpaSpecificationExecutor<Robot> {
    @Override
    @QueryHints(
        @QueryHint(name = "hint_name", value = "hint_value")
    )
    List<Robot> findAll(Specification<Robot> spec);
}

Though in this case, hints aren't dynamic.

Answer 2

maybe this discussion is a bit old but i had a similar issue, where i created a spefication for a findAll query. Within this specification it was not possible for me to add a query Hint. Therefore I added an base Repository where i could override the findAll method and add a query hint. how to create the base Repo is described here: https://www.baeldung.com/spring-data-jpa-method-in-all-repositories

for the queryHint:

    TypedQuery<T> query = this.getQuery(specification, pageable);
    ((CriteriaQueryTypeQueryAdapter<?>) query).addQueryHint(your hint)

Sometimes it is possible to add a Custom SQL Dialect that this is working, but that depends on the DB you are using.