JPA - Finding nested entities using combined criterias - jpa

Question

I have an entity named FileEntity which contains a list of reports of the type ReportEntity.
FileEntity has an field which determines, which user has created the file containing a number of reports.
#Entity
public class FileEntity {
#Id
private Long id;
#JoinColumn(name = "user")
#ManyToOne(optional = true)
#NotNull
private User user;
#OneToMany(cascade = CascadeType.ALL,
fetch = FetchType.EAGER,
orphanRemoval = true)
#NotNull
private List<Report> reports = new ArrayList<>(5);
...
}
#Entity
public class Report {
#Id
private Long id;
...
}
I am currently trying to fetch a single report with a given report ID and the ID of the person who issued the file containing the report. The combination is unique, so it should only return one report for a certain combination of report and user ID. But I am unable to retrieve a single result using the following criteria:
public Report findReportByUserAndReportId(Long reportId, Long userId) {
Objects.nonNull(reportId);
Objects.nonNull(userId);
try {
final CriteriaBuilder cb = entityManager.getCriteriaBuilder();
final CriteriaQuery<Report> cq = cb.createQuery(Report.class);
final Root<FileEntity> fileEntity = cq.from(FileEntity.class);
final Root<Report> report = cq.from(Report.class);
final Join<FileEntity, Report> join = fileEntity.join(FileEntity_.reports);
final Predicate[] predicates = new Predicate[]{
cb.equal(join.get("id"),
userId),
cb.equal(join.get(Report_.id),
reportId)};
cq.select(report).where(predicates);
return entityManager.createQuery(cq).getSingleResult();
} catch (NoResultException |
NonUniqueResultException ne) {
LOG.log(Level.WARNING,
"Could not find report: {0}",
ne.getMessage());
}
return null;
}
Has someone an idea what I am doing wrong?

Answer 1

First, don't use multiple roots here, because they generate a carthesian product of all the elements, without joining them. Use joins or Paths instead. Second, in the first predicate. join object denotes a Path of reports, not a user, therefore it doesnt' make sense to look for the userid there.
Root<FileEntity> fileEntity = cq.from(FileEntity.class);
Path<User> user = fileEntity.get(FileEntity_.user);
Join<FileEntity, Report> reports = fileEntity.join(FileEntity_.reports);
Predicate[] predicates = new Predicate[]{
cb.equal(user.get(User_.id),
userId),
cb.equal(reports.get(Report_.id),
reportId)};