title: objectdb select where query
body: <p>I attempt to select some instance using where clause</p>
  
  <pre><code>public static List&lt;RSSItem&gt; getRSSItem(int x1, int x2) {
       EntityManagerFactory emf = DBHandler.getEmf();
      EntityManager em = DBHandler.getEm(emf);
      String query =
              "SELECT items FROM RSSItem items "
              + "WHERE items.id &lt;= :x1 AND "
              + "items.id &gt;= :x2";
      List&lt;RSSItem&gt; results =
              (List&lt;RSSItem&gt;) em.createQuery(query).
              setParameter("x1", x1).
              setParameter("x2", x2).
              getResultList();
      return results;
  }
  </code></pre>
  
  <p>the RSSItem attributes :</p>
  
  <pre><code>@Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;
  String title;
  String link;
  String description;
  String pubdate;
  String content;
  HashMap&lt;String, Integer&gt; keyword = new HashMap();
  HashMap&lt;String, Integer&gt; keywordBefore = new HashMap();
  // TreeMap &lt;String, Integer&gt; keyword = new TreeMap();
  String feed;
  </code></pre>
  
  <p>the problem is it always return a list with 0 size. what's wrong with my select query?</p>