How to do this without 'distinct': Select Distinct(x) From x Left Join y Where y.attr = true

I'm stuck in a query, I'm using Spring Data JPA, JpaRepository and JpaSpecificationExecutor. So I have to use `Predicate`s from `CriteriaBuilder`. At the moment I simply do: ``` Specifications<MyEntity> spec = Specifications.where(MySpec.isTrue()); List<MyEntity> myEntities = myRepository.findAll(spec); ``` where MySpec.isTrue() is: ``` public static Specification<MyEntity> isTrue() { return new Specification<MyEntity>() { @Override public Predicate toPredicate(Root<MyEntity> root, CriteriaQuery<?> query, CriteriaBuilder cb) { SetJoin<MyEntity, JoinEntity> j = root.join(MyEntity.joinEntities, JoinType.LEFT); return cb.isTrue(j.get(JoinEntity_.attr)); } }; } ``` So this will of course result in this SQL: ``` SELECT e.* FROM MyEntity e LEFT OUTER JOIN JoinEntity j ON j.myEntityId = e.id WHERE j.attr = true ``` But I'm only interested in the unique set of `MyEntity`s. So in JPQL I'd write: ``` SELECT DISTINCT(e) FROM MyEntity e LEFT JOIN e.joinEntities j WHERE j.attr = true ``` Right now my solution is: ``` List<MyEntity> myEntities = myRepository.findAll(spec); Set<MyEntity> entitiesSet = new HashSet<MyEntity>(myEntities); ``` There must be a nicer way ;) How does it work with `CriteriaBuilder` (and `JpaSpecificationExecutor`)? The solution(s): The first idea was a simple distinct: ``` public static Specification<MyEntity> isTrue() { return new Specification<MyEntity>() { @Override public Predicate toPredicate(Root<MyEntity> root, CriteriaQuery<?> query, CriteriaBuilder cb) { SetJoin<MyEntity, JoinEntity> j = root.join(MyEntity.joinEntities, JoinType.LEFT); query.distinct(true); // <<-- HERE return cb.isTrue(j.get(JoinEntity_.attr)); } }; } ``` This works but kinda destroys the sense of those small Specification pieces. So I came up with a solution using a subquery. It may take some additional time, but for me it doesn't matter at the moment: ``` public static Specification<MyEntity> isTrue() { return new Specification<MyEntity>() { @Override public Predicate toPredicate(Root<MyEntity> root, CriteriaQuery<?> query, CriteriaBuilder cb) { Subquery<JoinEntity> subquery = query.subquery(JoinEntity.class); Root<JoinEntity> subRoot = subquery.from(JoinEntity.class); subquery.select(subRoot); subquery.where(cb.isTrue(subRoot.get(JoinEntity_.attr))); subquery.groupBy(subRoot.get(JoinEntity_.myEntity)); return cb.exists(subquery); } }; } ```