Question

美好的一天，我的问题将由两部分组成。所以，我有3个表：

A ， ABC ， CD

我想知道如何使用hibernate CriteriaQuery 实现以下查询：

SELECT DISTINCT a
FROM a
LEFT JOIN abc ON a.Id = abc.a_Id
LEFT JOIN cd ON cd.c_Id = abc.c_Id
WHERE a.name = "foo" or cd.name = "bar"

这一个（查询相同，但在这种情况下，我希望只有一列而不是完整行结果）：

SELECT DISTINCT a.Id
FROM a
LEFT JOIN abc ON a.Id = abc.a_Id
LEFT JOIN cd ON cd.c_Id = abc.c_Id
WHERE a.name = "foo" or cd.name = "bar"

Answer 1

这里有一个简单的方法：

public List<MyObject> listeOfMyObject() {
    EntityManager em;
    try {
        em = getEntityManager();
        Query query = em.createQuery("SELECT DISTINCT a FROM MyObject a LEFT JOIN abc ON a.Id = abc.a_Id LEFT JOIN cd ON cd.c_Id = abc.c_Id WHERE a.name = 'foo' or cd.name = 'bar'");
        return query.getResultList();
    } catch (Exception e) {
        return null;
    }
}

如果您使用的是参数，请使用：

public List<MyObject> listeOfMyObject() {
    EntityManager em;
    try {
        em = getEntityManager();
        Query query = em.createQuery("SELECT DISTINCT a FROM MyObject a LEFT JOIN abc ON a.Id = abc.a_Id LEFT JOIN cd ON cd.c_Id = abc.c_Id WHERE a.name = :a_name or cd.name = :cd_name");
        //set your parametres like that
        query.setParameter("c_name", "foo");
        query.setParameter("cd_name", "bar");
        return query.getResultList();
    } catch (Exception e) {
        return null;
    }
}

如果您只想获得一个结果：

public MyObject myObject() {
    EntityManager em;
    try {
        em = getEntityManager();
        Query query = em.createQuery("SELECT DISTINCT a FROM MyObject a LEFT JOIN abc ON a.Id = abc.a_Id LEFT JOIN cd ON cd.c_Id = abc.c_Id WHERE a.name = :a_name or cd.name = :cd_name");
        //set your parametres like that
        query.setParameter("c_name", "foo");
        query.setParameter("cd_name", "bar");
        return (MyObject) query.getSingleResult();
    } catch (Exception e) {
        return null;
    }
}

希望这可以帮到你。

Hibernate 5.2 Criteria Query（Join），选择特定列

1 个答案: