我想选择具有特定属性的实体。由于file
属性会返回byte[]
,这会降低应用程序的速度,因此无法检索整个实体。但它会抛出ClassCastException
。选择具有特定属性的实体时发生ClassCastException
这里是实体:
@NamedQuery(name = "findAllGarbage", query = "SELECT g.filename, g.description, g.uploadDate FROM Garbage g;")
@Entity
public class Garbage {
@Id
@GeneratedValue
@Column(nullable = false)
private Long id;
@Column(nullable = false)
private String filename;
@Column(nullable = false)
private String fileType;
@Column(nullable = false)
private String uploadDate;
@Column(nullable = false)
private String destroyDate;
@Lob
@Column(nullable = false)
private byte[] file;
@Column(nullable = false)
private String description;
//Getters and Setters...
下面是数据访问EJB。方法findAllGarbage()
是触发ClassCastException
的方法。
@Stateless(name = "ejbs/SearchEJB")
public class SearchEJB implements ISearchEJB {
@PersistenceContext
private EntityManager em;
public List<Garbage> findAllGarbage() {
Query query = em.createNamedQuery("findAllGarbage");
List<Garbage> gList = new ArrayList();
for (Object o : query.getResultList()) {
Garbage tmpG = new Garbage();
tmpG.setFilename(((Garbage) o).getFilename());
tmpG.setUploadDate(((Garbage) o).getUploadDate());
tmpG.setDescription(((Garbage) o).getDescription());
gList.add(tmpG);
}
return gList;
}
}
至于替代(我也更喜欢btw),OP提到,这不是一个选项,请参阅相关的问题+答案:http://stackoverflow.com/questions/5460476/issue-rendering- jpql-custom-query-results-into-a-jsf-page – BalusC 2011-03-30 00:10:59
for循环修复了类转换异常。谢谢。但sortBy函数不工作。 – sfrj 2011-03-30 08:30:31