How to do it with JPA Criteria API?

Question

我如何在JPA2中进行条件查询，这等效于使用和不使用元模型的JPQL？

SELECT p FROM Employee e JOIN e.phones p WHERE e=:empl

Answer 1

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Phone> criteriaQuery = cb.createQuery(Phone.class);
Root<Employee> employee = criteriaQuery.from(Employee.class);
CollectionJoin<Employee, Phone> phone = employee.join(Employee_.phones);
criteriaQuery.where(cb.equal(employee, empl);
criteriaQuery.select(phone);
TypedQuery<Phone> query = em.createQuery(criteriaQuery);
List<Phone> phones = query.getResultList();

That said, I see no point in replacing a simple, obvious JPQL query with the horrendous, unreadable lines of code above. Criteria queries are useful to dynamically construct queries, but JPQL shines for static queries like the one you have.