JPA itself doesn’t care whether the collection is initialized or not. When retrieving an Order from the database with JPA, JPA will always return an Order with a non-null list of OrderLines. Why: because an Order can have 0, 1 or N lines, and that is best modeled with an empty, one-sized or N-sized collection. … Read more
I had the same conclusions about these implementations. OpenJPA was/seemed buggy Hibernate had tons of libraries and seemed to have trouble with not lazy loading everything. Toplink ended up as my choice. It was not as flexible as Hibernate would have been but it works and I don’t have to install commons-logging. The one I … Read more
I might not understand your question. However, don’t you need something like below? @ManyToOne(fetch=FetchType.LAZY) @JoinColumn(name=”order_id”, nullable=false) Order order; here are some examples
This criteria set-up should do the trick: CriteriaBuilder cb = entityManager.getCriteriaBuilder(); CriteriaQuery<Employee> q = cb.createQuery(Employee.class); Root<Employee> root = q.from(Employee.class); q.select(root); List<String> parentList = Arrays.asList(new String[]{“John”, “Raj”}); Expression<String> parentExpression = root.get(Employee_.Parent); Predicate parentPredicate = parentExpression.in(parentList); q.where(parentPredicate); q.orderBy(cb.asc(root.get(Employee_.Parent)); q.getResultList(); I have used the overloaded CriteriaQuery.where method here which accepts a Predicate.. an in predicate in this case.
Returning a Map result using JPA Query getResultStream Since the JPA 2.2 version, you can use the getResultStream Query method to transform the List<Tuple> result into a Map<Integer, Integer>: Map<Integer, Integer> postCountByYearMap = entityManager.createQuery(“”” select YEAR(p.createdOn) as year, count(p) as postCount from Post p group by YEAR(p.createdOn) “””, Tuple.class) .getResultStream() .collect( Collectors.toMap( tuple -> ((Number) … Read more
It is there to specify another column as the default id column of the other table, e.g. consider the following TableA id int identity tableb_key varchar TableB id int identity key varchar unique // in class for TableA @JoinColumn(name=”tableb_key”, referencedColumnName=”key”)