带有@EmbeddedID和@Embeddable的EclipseLink复合密钥

Question

请求表是这样注释的。

@Entity
@Table( name = "REQUEST" )
public class Request implements Serializable {

  /**
  Different other columns and below is request note table
  **/
  @OneToMany( cascade = CascadeType.ALL, mappedBy = "request" )
  private List<RequestNote> requestNoteList;
}

接下来，我有一个包含请求id和注释id表的联接表

@Entity
@Table( name = "REQUEST_NOTE" )
public class RequestNote implements Serializable {


  @EmbeddedId
  protected RequestNotePK requestNotePK;
  @ManyToOne( optional = false, fetch = FetchType.LAZY )
  private Request request;
  @JoinColumn( name = "NOTE", referencedColumnName = "ID", insertable = false, updatable = false )
  @ManyToOne( optional = false, fetch = FetchType.EAGER )
  private Note note;
  }

现在我有了笔记表，它是普通表。它有自己的@SequenceGenerator

@Entity
@Table( name = "NOTE" )
public class Note implements Serializable {

  @Id
  @NotNull
  @GeneratedValue( generator = "NOTE_SEQ" )
  @SequenceGenerator( name = "NOTE_SEQ", sequenceName = "NOTE_SEQ", allocationSize = 1 )
  private String id;

  @OneToMany( cascade = CascadeType.ALL, mappedBy = "note" )
  private List<RequestNote> requestNoteList;

  }

现在，从用户界面，用户可以改变，添加或删除备注的请求。

当我从UI添加新的Note时，我有以下代码。在这里，我已经有了请求Id，但是Notes Id必须生成并保存到Join table(request_note)表，我得到了错误。

//Create New Note
        Note newNote = new Note();
        newNote = noteFromUI;
        //something like that very common


          //Creating new Request Note row
          RequestNote newRequestNote = new RequestNote();
          newRequestNote.setNote(noteFromUI);
          newRequestNote.setRequest(getRequest());
          RequestNotePK requestNotePK =
                  new RequestNotePK(getRequest().getId(), noteFromUI.getId());
          newRequestNote.setRequestNotePK(requestNotePK);

          getRequest().addRequestNoteList(newRequestNote);

我现在的问题或错误是。

null

我如何让我的连接表请求Note表知道，它必须使用新创建的id从Note表到它的连接表。

Answer 1

如果您使用的是JPA2.0，您可以使用derrived ID，特别是@mapsid，如下所示：

  @MapsId("id")//attribute name from within RequestNotePK 
  @JoinColumn( name = "NOTE", referencedColumnName = "ID")
  @ManyToOne( optional = false, fetch = FetchType.EAGER )
  private Note note;

如果没有，则必须手动将note中的id设置为RequestNotePK实例。代码中缺少的是，只有在调用Flush时才保证设置ID：

  Note newNote = new Note();
  newNote = noteFromUI;
  em.persist(newNote);//ID would be set if the sequence allows a pre allocation
  em.flush();//issues statements and will set sequence values

在此之后，将设置note.id，并可用于设置requestnote.requestnotepk.id