JPA How to build a join criteria query - mysql

Question

I have the following situation 3 tables, person, job, category.
Person has a job and Job has a category. How do I get the person records from the same category.
public List<Person> findPplByCategory(Category category) {
javax.persistence.criteria.CriteriaBuilder cb = getEntityManager().getCriteriaBuilder();
javax.persistence.criteria.CriteriaQuery cq = getEntityManager().getCriteriaBuilder().createQuery();
javax.persistence.criteria.Root<Person> e = cq.from(Person.class);
javax.persistence.criteria.Root<Job> a = cq.from(Job.class);
//...not sure how to create the query here..
}

Answer 1

This is easy to do using a JPQL query
String query = "select P from Person P join P.job J join J.category C where C = :cat"
List<Person> = entitiyManager.createQuery(query, Person.class).setParameter("cat", myCategory).getResultList();
Some assumptions:
One Person has one Job
One Job has one Category
Person's job field is named job
Job's category field is named category

Answer 2

haven't tested but may be something like
CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<Person> q = cb.createQuery(Person.class);
Root<Person> person = q.from(Person.class);
Join<Person,Job> job = person.join(Person_.job);
Predicate predicate = cb.conjunction();
Predicate p = cb.equal(job.get(Job_.category), cat);
predicate = cb.and(p);
q.where(predicate);
q.select(person);
TypedQuery<Person> tq = entityManager.createQuery(q);
List<Person> all = tq.getResultList();
return all;

Answer 3

javax.persistence.criteria.CriteriaBuilder cb = getEntityManager().getCriteriaBuilder();
javax.persistence.criteria.CriteriaQuery cq = getEntityManager().getCriteriaBuilder().createQuery();
javax.persistence.criteria.Root<Person> e = cq.from(perdon.class);
cq.where(cb.equal(e.get("idCompany").get("idCategory"), cat));
cq.orderBy(cb.desc(e.get("idPerson")));
return getEntityManager().createQuery(cq).getResultList();

Answer 4

my version is:
CriteriaBuilder cb = getEntityManager().getCriteriaBuilder();
CriteriaQuery<Person> cq = cb.createQuery(Person.class);
Root<Person> root = cq.from(Person.class);
Join<Person,Job> job = root.join(Person_.job);
Join<Job,Category> category =car.join(Car_.category).where(cb.equal(job.get(Job_.category).get(Category_.name),"your category"));
cq.select(root);
TypedQuery<Person> query = getEntityManager().createQuery(cq);
return query.getResultList();
Here you have that Person is one-to-one with Job and the latter is one-to-one with Category :) You will receive you all persons which is in specified category of job.