Spring Data Jpa and Specification - ManyToMany

Question

I have a similar problem with this one: Spring Data Jpa and Specification - how to work with ManyToOne and ManyToMany relations?

I have 3 tables: actor, movie and mactors (the join table for movies and actors) with spring boot, hibernate-jpamodelgen

@Entity
public class Actor {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;

...
}

@Entity
public class Movie implements BaseId {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;
....

}

I would like to get those movies where 2 or more actors have been in together. Something like this query:

select * from movie 
    join mactors on movie.id = mactors.movie
    where mactors.actor = x and mactors.actor = y and ...;

public static Specification<Movie> findMoviesByActors(List<Long> actors) {
    return (root, criteriaQuery, criteriaBuilder) -> {
        ...
        return ...
    };
}

I have no clue what next.

Any hint would be appreciated. Thanks

Answer 1

It seems that my original SQL query was wrong. An working SQL would be:

select distinct * from movie 
    join mactors on movie.id = mactors.movie_id 
    where mactors.actor_id in (x, y, z...)
group by movie.title
having count(movie.id) >= numberOfActors;

The code bellow works:

public static Specification<Movie> findByActorsId(List<Long> actorIds) {
    return new Specification<Movie>() {
        @Override
        public Predicate toPredicate(Root<Movie> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
            Join<Movie, Actor> join = root.join(Movie_.actors);

            Predicate actorIdPredicate = cb.disjunction();
            for(Long aid : actorIds) {
                actorIdPredicate.getExpressions().add(cb.equal(join.get(Actor_.id), aid));
            }

            Expression<Long> count = cb.count(root.get(Movie_.id));
            CriteriaQuery<Movie> q = (CriteriaQuery<Movie>) query.distinct(true).groupBy(root.get(Movie_.title)).
                    having(cb.greaterThanOrEqualTo(count, new Long(actorIds.size()));

            return actorIdPredicate;
        }
    };
}

I didn't manage to get in clause to work, but I did an OR in a loop...

Any tips to improve are welcome :)