1 Reply Latest reply on Jan 29, 2007 4:45 PM by fhh

    Bug? @Inheritance(strategy=JOINED) AND @DiscriminatorValue d

    fhh Jan 29, 2007 3:59 PM

      Hello!

      It seems that the the JBoss EJB3/Hibernate stuff ignores the @DiscriminatorValue annotation on JOIND inheritances:

      @Entity
@Inheritance(strategy=JOINED)
public abstract class parent {

 @Id
 Integer id;

}

@Entity
@DiscriminatorValue("child")
public class child extends parent {

 private String value;

}


      If I read the documentation correctly the table parent should have a column DTYPE and for every persited child object it should have the value child.

      I know this value is not actually necessary since I could simply inner join child and parent but this becomes inefficient if more than a couple of classes extend parent. And it is unefficient if all I'm interested in is some aggregation of values in parent.

      I am not sured if support for discriminator column is required by the specs but Toplink ( http://www.oracle.com/technology/products/ias/toplink/jpa/howto/use-inheritance.html ) and Kodo http://docs.solarmetric.com/full/html/ejb3_overview_mapping_discrim.html support this. To me this seems like a bug because it makes the inheritance strategy JOINED far less useful.

      Regards

      Felix[/url]

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        • 1. Re: Bug? @Inheritance(strategy=JOINED) AND @DiscriminatorVal
          fhh Jan 29, 2007 4:45 PM (in response to fhh)

          Sorry, I have found the Hibernate bug describing this: http://opensource.atlassian.com/projects/hibernate/browse/ANN-140?page=all

          (It is amazing that you always find the bug report only after you tried to describe the problem yourself.)

          Since I don't know anything about the hibernate sources I will not even try to supply the 3k lines mentioned in the bug report but I have a dirty little workaround:

          @Entity
@Inheritance(strategy=JOINED)
//@DiscriminatorColumn(name="YOUR_DTYPE")
public abstract class parent {

 @Id
 Integer id;

 @Column(name="YOUR_DTYPE",length=31)
 public String getDiscriminatorValue() {

 DiscriminatorValue discriminatorValueAnnotation = this.getClass().getAnnotation(DiscriminatorValue.class);

 if (discriminatorValueAnnotation != null) {
 return discriminatorValueAnnotation.value();
 }

 return this.getClass().getSimpleName();
 }

 public void setDiscriminatorValue(String dummy) {
 }

}


          It is double plus unbeautiful but it works. Should this ever be fixed you can simply remove the workaround and everything should work as expected.

          Regards

          Felix


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