Hibernate 5.2條件查詢（Join），選擇具體的列

Question

好日子，我的問題將由兩部分組成。所以，我有3個表：

一個，ABC，CD

我不知道我可以使用Hibernate CriteriaQuery中執行以下查詢：

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" 

而這一次（查詢是相同的，但在這種情況下，我想只有一列而不是全行結果）：

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

這裏一個簡單的方法：

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; 
    } 
} 

如果您使用的參數應用使用：

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; 
    } 
} 

如果你想獲得結果只有一個：

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; 
    } 
} 

希望這可以幫到你。