package ejava.examples.orm.rel.annotated;
   
   import javax.persistence.*;
   
   import org.slf4j.Logger;
   import org.slf4j.LoggerFactory;
   
   import ejava.examples.orm.rel.MediaCopyPK;
   
  /**
   * This class provides an example of a ManyToOne mapping. The media copy owns
   * the relationship to the media. Therefore the foreign key to media is within
   * the media copy database table.<p/>
   * 
   * This class has an unrelated technical issue worth mentioning. 
   * Everything would have worked out fine if we created a simple primary key
   * field for the media copy and a separate foreign key to the media. Instead, 
   * we pretended to encounter a composite primary key where one of the values
   * doubled as the foreign key to the media.<p/>
   * 
   * <pre>
   * MediaCopy (pk=MEDIACOPY_MID + COPYNO)
   *     MEDIACOPY_MID (fk to Media.MEDIA_ID) 
   *     COPYNO
   *     ...
   * Media (pk=MEDIA_ID)
   *     MEDIA_ID
   *     ...
   * </pre>
   * 
   * The MediaCopy now has two uses for the MEDIACOPY_MID column. One as a primary
   * key (part of a compound primary key) and the other as the foreign key to the Media.
   * We need to make sure the provider preserves the semantics of the primary key while
   * reusing it from the foreign key.
   * 
   * This implementation will use the JPA 1.0 technique of mapping both the 
   * primary and foreign key properties to the same column and then mark the 
   * foreign key as READ-ONLY using the insertable and updatable properties
   * of the @Column.
   */
  
  @Entity @Table(name="ORMREL_MEDIACOPY")
  @IdClass(MediaCopyPK.class)
  public class MediaCopy {
      private static final Logger log = LoggerFactory.getLogger(MediaCopy.class);
      @Id //mapped to COPY_NO by IdClass
      private int copyNo;    
      @Id //mapped to MEDIACOPY_MID by IdClass
      private long mediaId;    
      @ManyToOne
      @JoinColumn(name="MEDIACOPY_MID", //mapped same as mediaId property
              insertable=false, updatable=false) //makes column read-only
      private Media media;
      
      protected MediaCopy() { log.debug(super.toString() + ": ctor()"); }
      public MediaCopy(Media media, int copyNo) {
          log.debug(super.toString() + ": ctor() mediaId="
                  + media.getId() + ", copyNo=" + copyNo);
          setMedia(media);
          setMediaId(media.getId());
          setCopyNo(copyNo);
      }    
  
      public int getCopyNo()                { return copyNo; }    
      private void setCopyNo(int copyNo)    { this.copyNo = copyNo; }
      
      public long getMediaId()              { return mediaId; }
      private void setMediaId(long mediaId) { this.mediaId = mediaId; }
      
      public Media getMedia()               { return media; }    
      private void setMedia(Media media)    { this.media = media; }
  
      private String myInstance() {
          String s=super.toString();
          s = s.substring(s.lastIndexOf('.')+1);
          return s;
      }
  
      public String toString() {
          return myInstance() +
              ", mediaId=" + mediaId +
              ", copyNo=" + copyNo +
              ", media=" + media;
      }
  }