JPA规范：选择列表属性包含具有特定值的项目的项目

Question

I am trying to solve the following problem with JPA specifications:

Consider the following classes:

public class Language {
    private String name;
    ...
}

public class Person {
    private List<Language> languages;
    ...
}

How do I select all Person s, that speak a language with name x ? I am looking for a solution using the CriteriaBuilder , which should generate a Predicate that I can 'and' together with other predicates.

Thanks in advance.

Answer 1

It is actually pretty easy:

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Person> query = cb.createQuery(Person.class);
Root<Person> root = query.from(Person.class);
ListJoin<Person, Language> langJoin = root.join(Person_.langs);
query.where(cb.equal(langJoin.get(Language_.name), lang));

So you basically join the languages via corresponding association and then add an equals predicate matching the required attribute of the joined entity with your criteria.