如何使用Criteria子句進行JPA查詢？

Question

首先，我想要做一個查詢像

"select count(*) from Post p where p.tag in (tagArray) " 

其中tagArray是「‘標籤1’，‘標籤2’，‘標籤3’」那麼我會喜歡做PAGINATE查詢：

query.setFirstResult(int1).setMaxResult(int2); 

我不知道如何編寫這個查詢。我搜索了帖子，找不到答案，那麼有人可以給我任何建議嗎？謝謝。

Answer 1

非常感謝您！遵照你的指示，我已經這樣做了，有點複雜。

public List<Post> findPostBySitePaged(Set sites, Page page) { 
    List<Post> result = new ArrayList<Post>(); 
    if (sites == null || sites.size() == 0) return result; 

    try { 
     CriteriaBuilder builder = em.getCriteriaBuilder(); 

     CriteriaQuery<Long> cQuery = builder.createQuery(Long.class); 
     Root<Post> root = cQuery.from(Post.class); 

     CriteriaQuery<Long> select = cQuery.select(builder.count(root)); 
     select.where(root.get("site").in(sites)); 

     TypedQuery<Long> typedQuery = em.createQuery(select); 
     Long t = typedQuery.getSingleResult(); 

     int tot = t.intValue()/page.getPageSize() + ((t.intValue() % page.getPageSize()) == 0 ? 0 : 1); 
     page.setTotal(tot); 

     CriteriaQuery<Post> criteriaQuery = builder.createQuery(Post.class); 
     root = criteriaQuery.from(Post.class); 
     criteriaQuery.select(root).where(root.get("site").in(sites)).orderBy(builder.desc(root.get("createDate"))); 

     TypedQuery<Post> postQuery = em.createQuery(criteriaQuery); 
     postQuery.setFirstResult((page.getCurrent() - 1) * (page.getPageSize())).setMaxResults(page.getPageSize()); 

     result = postQuery.getResultList(); 

    } catch (Exception e) { 
     log.error(e.getMessage()); 
    } 

    return result; 
} 

Answer 2

這裏的示例代碼：

// get an entity manager 
EntityManagerFactory emf = Persistence.createEntityManagerFactory("jpaManager"); 
EntityManager em = emf.createEntityManager(); 
// create query 
Query query = em.createQuery("select count(*) from Post p where p.tag in (tagArray)") // use parameters here when necessary 
      .setFirstResult(int1) 
      .setMaxResults(int2); 
// get result 
query.getResultList(); 

更新：

如果你想創建的條件查詢，試試這個：

CriteriaBuilder builder = em.getCriteriaBuilder(); // em is as the same the the above 
CriteriaQuery<Post> query = builder.createQuery(Post.class); 
Root<Post> post = query.from(Post.class); 
query.select(post).where(post.get("tag").in("tag1", "tag2", "tag3")); // or pass a tag collection to `in` method 
TypedQuery<Post> typedQuery = em.createQuery(query); 
List<Post> results = typedQuery.setFirstResult(int1).setMaxResults(int2) 
        .getResultList();