objectdb选择where查询

Question

我尝试使用where子句选择一些实例

public static List<RSSItem> getRSSItem(int x1, int x2) {
     EntityManagerFactory emf = DBHandler.getEmf();
    EntityManager em = DBHandler.getEm(emf);
    String query =
            "SELECT items FROM RSSItem items "
            + "WHERE items.id <= :x1 AND "
            + "items.id >= :x2";
    List<RSSItem> results =
            (List<RSSItem>) em.createQuery(query).
            setParameter("x1", x1).
            setParameter("x2", x2).
            getResultList();
    return results;
}

RSSItem属性：

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
String title;
String link;
String description;
String pubdate;
String content;
HashMap<String, Integer> keyword = new HashMap();
HashMap<String, Integer> keywordBefore = new HashMap();
// TreeMap <String, Integer> keyword = new TreeMap();
String feed;

问题是它总是返回一个大小为0的列表。我的select查询出了什么问题？

Answer 1

值为x1 = 1和x2 = 500时，查询变为...

SELECT items FROM RSSItem items
 WHERE items.id <= 1 
   AND items.id >= 500

因为没有id同时为less or equal to 1和greater or equal to 500，所以查询将不会给出匹配结果。你想要的可能是；

String query =
        "SELECT items FROM RSSItem items "
        + "WHERE items.id >= :x1 AND "
        + "items.id <= :x2";

包含示例数据的...which将找到1到500之间(包括1和500)的所有id。