Specification OR clause, in and isEmpty/isNull - spring-boot

Question

I have workers that have competences (driving licenses and such) and then there are mechanisms that require certain competences. Sometimes the mechanisms require no competences at all.
Currently I have a Specification with an in clause that works fine, but I would like it to also send out mechanisms that require no competences to operate.
public static Specification<Mechanism> hasCompetences(String searchTerm) {
return (root, query, criteriaBuilder) -> {
query.distinct(true);
List<String> list = new ArrayList<>(Arrays.asList(searchTerm.split(",")));
return root.join("competences").get("name").in(list);
};
}
If I have 3 mechanisms with competences like
Car | B-Category |
Van | C-Category |
Bicycle |(no data here) |
After requesting mechanisms?competences=B-Category it returns Car as expected, but I would like to get the Bicycle too.
Or is there a way to get all all mechanisms that don't require competences? I tried mechanisms?competences= but that returned [].
Edit:
This is where I'm at right now:
public static Specification<Mechanism> hasCompetences(List<String> list) {
return (root, query, cb) -> {
query.distinct(true);
return cb.or(
cb.isEmpty(root.join("competences")),
root.join("competences").get("name").in(list)
);
};
}
But the isEmpty is giving me this error:
java.lang.IllegalArgumentException: unknown collection expression type [org.hibernate.query.criteria.internal.path.SetAttributeJoin]
Edit2:
public static Specification<Mechanism> hasCompetences(List<String> list) {
return (root, query, cb) -> {
query.distinct(true);
Join<Mechanism, Set<Competence>> competences = root.join("competences", JoinType.LEFT);
return cb.or(
root.join("competences").get("name").in(list),
cb.isEmpty(competences)
);
};
}
Error:
unknown collection expression type [org.hibernate.query.criteria.internal.path.SetAttributeJoin];

Answer 1

You have 2 errors:
The criteria to match empty collection is cb.isEmpty(root.get("competences"))
You need to specify left join. root.join("competences", JoinType.LEFT)
Without the second amendment, you make an inner join, so you will never retrieve Mechanisms with empty competences.
Update
You proposed
Join<Mechanism, Set<Competence>> competences = root.join("competences", JoinType.LEFT);
return cb.or(
root.join("competences").get("name").in(list),
cb.isEmpty(competences)
);
isEmpty won't work on SetAttributeJoin (the result of root.join) - look point 1. above
Try
Join<Mechanism, Set<Competence>> competences = root.join("competences", JoinType.LEFT);
return cb.or(
competences.get("name").in(list),
cb.isEmpty(root.get("competences"))
);