在JPA中使用TypedQuery而不是普通的Query

Question

是否可以将此Query作为TypedQuery编写,让两个Long运行到一个内部有两个公共Long字段的Object中.

    Query q = em.createQuery(
            "SELECT c.id, COUNT(t.id) " +
            "FROM PubText t " +
            "JOIN t.comm c " +
            "WHERE c.element = ?1 " +
            "GROUP BY c.id");
    q.setParameter(1, e);
    List<?> rl = q.getResultList();
    Iterator<?> it = rl.iterator();
    HashMap<Long, Long> res = new HashMap<Long, Long>();
    while (it.hasNext()) {
        Object[] n = (Object[]) it.next();
        res.put((Long)n[0], (Long)n[1]);
    }
    return res;

Answer 1

JPA只为此提供了一个功能 - 构造函数表达式:

Query q = entityManager.createQuery("SELECT NEW com.example.DTO( c.id, COUNT(t.id)) FROM ...");
List<DTO> dtos = q.getResultList();

您的DTO课程可以是POJO.它需要的是一个接受2 Long秒的公共构造函数.请注意,您必须在NEW运营商之后提供您班级的完全合格的名称.

Answer 2

新代码现在看起来像这样.谢谢你的帮助.

    TypedQuery<CommUsed> q = em.createQuery(
        "SELECT new CommUsed(c.id,COUNT(t.id)) " +
        "FROM PubText t " +
        "JOIN t.comm c " +
        "WHERE c.element = ?1 " +
        "GROUP BY c.id", CommUsed.class);
    q.setParameter(1, e);
    HashMap<Long, Long> res = new HashMap<Long, Long>();
    for (CommUsed u : q.getResultList())
        res.put(u.commID, u.cnt);