JPA标准加入OneToMany表where子句不起作用

Question

我有两个表。

CREATE TABLE public.question 
(
    id  SERIAL PRIMARY KEY 
    , day  VARCHAR(2)  NOT NULL 
    , month VARCHAR(2)  NOT NULL 
    , year  VARCHAR(4)   NOT NULL 
); 

CREATE TABLE public.question_translation 
(
    id SERIAL PRIMARY KEY 
    , question_id INT REFERENCES public.question(id) NOT NULL 
    , question_text TEXT        NOT NULL 
    , language  VARCHAR(2)       NOT NULL 
); 

现在我想创建条件来检索问题。 SQL是这样的：

SELECT * FROM question q LEFT JOIN question_translation qt ON q.id = qt.question_id WHERE qt.language = 'en'

在Java中使用JPA规定 - 它看起来像这样：

@Override 
public Collection<Question> findByMonthYear(String month, String year, String locale) { 
    EntityManager em = sessionFactory.createEntityManager(); 
    CriteriaBuilder builder = em.getCriteriaBuilder(); 
    CriteriaQuery<Question> criteriaQuery = builder.createQuery(Question.class); 

    List<Predicate> predicates = new ArrayList<>(); 

    Root<Question> questionRoot = criteriaQuery.from(Question.class); 
    ListJoin<Question, QuestionTranslation> questionTranslationJoinRoot = questionRoot.join(Question_.questionTranslation, JoinType.LEFT); 

    predicates.add(builder.equal(questionRoot.get(Question_.month), month)); 
    predicates.add(builder.equal(questionRoot.get(Question_.year), year)); 
    predicates.add(builder.equal(questionTranslationJoinRoot.get(QuestionTranslation_.language), locale)); 

    criteriaQuery.select(questionRoot).where(predicates.toArray(new Predicate[]{})); 

    TypedQuery<Question> query = em.createQuery(criteriaQuery); 

    String queryString = query.unwrap(Query.class).getQueryString(); 

    return query.getResultList(); 
} 

我使用ListJoin因为在元模型Question_.class我得到这一行：

public static volatile ListAttribute<Question, QuestionTranslation> questionTranslation; 

但这一个返回我问题类与列表QuestionTranslation两个条目，其中语言字段等于en和de值。但是我指定where子句只返回一个条目，其中语言等于en的值。我的代码有什么问题？

更新＃1：

我有第二种情况。

还有一个表：

CREATE TABLE public.user_answer 
(
    uuid  VARCHAR(36) PRIMARY KEY 
    , user_uuid VARCHAR(36) REFERENCES public.users(uuid) NOT NULL 
    , question_id INT   REFERENCES public.question(id) NOT NULL 
    , answer  TEXT          NOT NULL 
); 

，我想做出这样的SQL：

SELECT * FROM user_answer ua LEFT JOIN question q on ua.question_id = q.id LEFT JOIN question_translation qt ON q.id = qt.question_id WHERE qt.language = 'en' AND ua.user_uuid = '00000000-user-0000-0000-000000000001' AND q.month = '01' AND q.day = '01' AND q.year = '2016';

在Java中使用JPA规定 - 它看起来像这样：

@Override 
public UserAnswer findByDayMonthYear(String day, String month, String year, User user, String locale) { 
    EntityManager em = sessionFactory.createEntityManager(); 
    CriteriaBuilder builder = em.getCriteriaBuilder(); 
    CriteriaQuery<UserAnswer> criteriaQuery = builder.createQuery(UserAnswer.class); 

    List<Predicate> predicates = new ArrayList<>(); 

    Root<UserAnswer> userAnswerRoot = criteriaQuery.from(UserAnswer.class); 
    Join<UserAnswer, Question> questionJoin = userAnswerRoot.join(UserAnswer_.question); 
    ListJoin<Question, QuestionTranslation> questionTranslatJoin = questionJoin.join(Question_.questionTranslation); 

    predicates.add(builder.equal(builder.treat(questionJoin, Question.class).get(Question_.day), day)); 
    predicates.add(builder.equal(builder.treat(questionJoin, Question.class).get(Question_.month), month)); 
    predicates.add(builder.equal(builder.treat(questionJoin, Question.class).get(Question_.year), year)); 
    predicates.add(builder.equal(builder.treat(questionTranslatJoin, QuestionTranslation.class).get(QuestionTranslation_.language), locale)); 
    predicates.add(builder.equal(userAnswerRoot.get(UserAnswer_.user), user)); 

    criteriaQuery.select(userAnswerRoot).where(predicates.toArray(new Predicate[]{})); 

    TypedQuery<UserAnswer> query = em.createQuery(criteriaQuery); 

    String queryString = query.unwrap(Query.class).getQueryString(); 

    return query.getSingleResult(); 
} 

在这种情况下，问题列出了包含两个带有languag的QuestionTranlsation项目es en和de，但我只需要一个QuestionTranlsation条目，其语言等于en。

我在这种情况下要做什么？

Answer 1

这是可能的JPA 2.1功能JOIN ON

看How to do JOIN ON query using Criteria API