如何在类型化查询中制定 JOIN？

Question

我想创建一个类型化的查询。

TypedQuery<PubThread> query = em.createQuery(queryString, PubThread.class);
query.setParameter("threadId", threadId);
List<PubThread> otherPubThreads = query.getResultList();

queryString中是如下SQL（目前没有param和静态选择值）

SELECT pt2 FROM pubthread pt2   
JOIN pub_pubthread ppt2 ON pt2.id = ppt2.pubThreads_id  
JOIN pub p2 ON ppt2.pups_id = p2.id     
JOIN pubcategory pc2 ON p2.pubCategoryId = pc2.id   
WHERE pt2.id != 1 and EXISTS (      
    SELECT DISTINCT(pt.id) 
    FROM pubthread pt       
    JOIN pub_pubthread ppt ON pt.id = ppt.pubThreads_id         
    JOIN pub p ON ppt.pups_id = p.id        
    JOIN pubcategory pc ON p.pubCategoryId = pc.id      
    WHERE pc2.id = pc.id and pt.id = 1  
)

如果我将字符串限制为一个简单的选择：SELECT Distinct(pt2.id), pt2.name FROM pubthread pt2，它确实有效。一旦我向它添加一条 JOIN 行，它就会抱怨。如何在 JPA 中正确查询 JOINS？错误是： org.hibernate.hql.internal.ast.QuerySyntaxException: unexpected token: ON near line 1, column 81 [SELECT pt2 FROM com.brayan.webapp.model.PubThread pt2 JOIN pub_pubthread ppt2 ON pt2.id = ppt2.pubThreads_id ]

毫无疑问，条件查询会更好。我接受它作为解决方案空间的一部分。

Answer 1

知道了。请参阅下面的完整连接示例。它包括：

• 多个连接（连接链）
• 子查询
• 连接表上的谓词相关/等式，而不是根表。

我还为其他人评论了过时的代码行，看看这是什么错误的方法。

CriteriaBuilder criteriaBuilder = em.getCriteriaBuilder(); CriteriaQuery mainQuery = criteriaBuilder .createQuery(PubThread.class);

    // 1) MainQuery
    // Create the FROM
    Root<PubThread> rootPubThread = mainQuery.from(PubThread.class);
    // Create the JOIN from the first select: join-chaining. You only need the return for ordering. e.g. cq.orderBy(cb.asc(categoryJoin.get(Pub_.title)));
    Join<Pub, PubCategory> categoryJoin = rootPubThread.join(PubThread_.pups).join(Pub_.pubCategory);
    // Create the WHERE
    mainQuery.where(criteriaBuilder.not(criteriaBuilder.equal(rootPubThread.get(PubThread_.id), threadId)));
    // Create the SELECT, at last
    mainQuery.select(rootPubThread).distinct(true);

    // 2) Subquery
    Subquery<PubThread> subquery = mainQuery.subquery(PubThread.class); 
    Root<PubThread> rootPubThreadSub = subquery.from(PubThread.class); 
    //subquery.where(criteriaBuilder.equal(rootPubThread.get(PubThread_.id), threadId));
    Join<Pub, PubCategory> categoryJoinSub = rootPubThreadSub.join(PubThread_.pups).join(Pub_.pubCategory);
    subquery.select(rootPubThreadSub);

    //Predicate correlatePredicate = criteriaBuilder.equal(rootPubThreadSub.get(PubThread_.id), rootPubThread);
    Predicate correlatePredicate = criteriaBuilder.and(
            //criteriaBuilder.equal(rootPubThreadSub.get(PubThread_.id), rootPubThread),
            criteriaBuilder.equal(categoryJoinSub.get(PubCategory_.id), categoryJoin.get(PubCategory_.id)),

            criteriaBuilder.equal(rootPubThreadSub.get(PubThread_.id), threadId)
            );
    subquery.where(correlatePredicate);     

    //Predicate correlatePredicate = criteriaBuilder.equal(rootPubThreadSub.get(PubThread_.id), rootPubThread);
    Predicate mainPredicate = criteriaBuilder.and(
            criteriaBuilder.not(criteriaBuilder.equal(rootPubThread.get(PubThread_.id), threadId)),
            criteriaBuilder.exists(subquery)
            );
    //cq.where(criteriaBuilder.exists(subquery));
    mainQuery.where(mainPredicate);

Answer 2

当您调用 createQuery 时，您必须编写 HQL 而不是 SQL（您的 queryString 不是 HQL）。
在 HQL 中，您必须根据映射实体连接对象。
如果您还需要 SQL 查询，请使用 createNativeQuery 方法。
有关如何创建 HQL 查询，请参阅 documentation。