Using inheritance to model summary/details pattern

fedot · **Joined:** Thu Dec 15, 2005 2:30 pm **Posts:** 10

I have a web page that first displays a list of items (showing only a "summary" of items' properties), where each item links to a "details" page. What I am trying to do is to only load the "summary" fileds on the first page, but go ahead and load all the remaining fileds for the item on the "details" page.

I am trying to achieve that by using object inheritance as follows:

Code:

@Entity(access=AccessType.FIELD)
@Table(name="documents")
public class DocumentSummary {
  @Id private Long id;
  @Column(name="id") private Date date;
  @Column(name="name") private String name;
  ...
}

@Entity(access=AccessType.FIELD)
@Table(name="documents")
public class DocumentDetails extends DocumentSummary {
  @Column(name="data") private byte[] data;
  ...
}

But I get the following error: "org.hibernate.AnnotationException: No identifier specified for entity: DocumentDetails"

After reading through the documentation I then tried changing @Entity to @EmbeddableSuperclass on DocumentSummary. But now whenever I try to load DocumentSummary objects, for some reason "data" column DOES get pulled in (according to SQL shown with hibernate.show_sql=true), even though it is not part of DocumentSummary but DocumentDetails instead.

Am I doing something wrong?

Goonie · **Posted:** Tue Dec 20, 2005 3:38 pm

Yes, you haven't got defined a column for your id (instead, you are mapping a Date to your id column - is this really what you want?).

Also, look at the @Inheritance annotation, which might be required (I don't know exactly).

emmanuel · **Posted:** Tue Dec 20, 2005 4:00 pm

the lightweight pattern is currently not supported through annotations, but you can use projections select new Summary(i.name, i.price) from Item i