JPA：如何选择@Embeddable类

Question

我将从@Embeddeble Class Certification中选择所有列。但我不能选择它。如何选择可嵌入类。

@Entity
public class Department implements Serializable {


  private static final long serialVersionUID = 1L;
  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  private Long id;
  private String name;

  @ElementCollection
  @CollectionTable(name = "Certification", joinColumns = {@JoinColumn(name="user_id")})
  private List<Certification> certifications = new ArrayList<Certification>();

  public List<Certification> getCertifications() {
      return certifications;
  }

  public void setCertifications(List<Certification> certifications) {
      this.certifications = certifications;
  }


  public String getName() {
      return name;
  }

  public void setName(String name) {
      this.name = name;
  }

  .....

@嵌入式类认证

@Embeddable
public class Certification{

  private String name;
  private String certArt;

  public String getName() {
      return name;
  }

  public void setName(String name) {
      this.name = name;
  }



  public String getCertArt() {
      return certArt;
  }

  public void setCertArt(String certArt) {
      this.certArt = certArt;
  }

  ......

如果运行ResultService，则会出现以下异常：

原因:Java . lang . illegalargumentexception:在EntityManager中创建查询时出现异常:异常描述:编译查询时出错[从认证c中选择c]。未知的实体类型[认证]。

如何选择@Embeddeble类？

Answer 1

您需要通过真实的实体类(即< code>Department)检索< code>Certification。一个示例查询如下:

   select cer from Department dep join dep.certifications cer

或者，您可能希望检索符合条件的部门实体，然后使用它们获取证书。