Unable to read Inherited class instances with DataNucles JDO

Question

I was unable to read the full inherited class instances as described in following URL

http://www.datanucleus.org/products/datanucleus/jdo/orm/inheritance.html

Following describes the mapping of classes.

@PersistenceCapable(detachable = "true")
@Discriminator(strategy=DiscriminatorStrategy.CLASS_NAME)
@Inheritance(strategy=InheritanceStrategy.NEW_TABLE)
public class IdeaItem {

    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    @Column(jdbcType = "INTEGER", length = 11)
    private long id;

    @Column(name="IDEAID")
    private Idea idea;

    @Column(jdbcType = "INTEGER", length = 11)
    private long showOrder;

 }

 @PersistenceCapable(detachable = "true") 
 @Inheritance(strategy=InheritanceStrategy.NEW_TABLE)
 public class IdeaItemText extends IdeaItem {

    @Column(jdbcType = "VARCHAR", length = 500) 
    private String text;

 }

Data saving part working fine. I inserted "IdeaItemText" object and both "IdeaItem" and "IdeaItemText" tables got updated successfully.

Now I need to read Subclasses by putting "IdeaItem" as an Extent. I executed the following code.

 Extent items = getPersistenceManager().getExtent(IdeaItem.class,true);
 javax.jdo.Query q = getPersistenceManager().newQuery(items);
 List data = (List)q.execute();

As in the JDO docs, this should return the whole object graph. But this is not returning any record. When I check the log, I found that it searching for a reacord where Discriminator Value equals to "com.mydomain.IdeaItem" which does not exists. When I removed the Discriminator annotation I got all the records in the table. Even though how I access the sub classes attributes ? Furthermore how I query subclass attributes with the base class Extent ?

DataNucleus DataNucleus · Accepted Answer · 2013-05-23T15:59:44

So you didn't let the persistence mechanism know about the subclass (whether that is using auto-start mechanism, persistence.xml, calling pm.getExtent on the subclass, or simply instantiating the subclass.class). It can only query classes that it is "aware of"

Unable to read Inherited class instances with DataNucles JDO

1 Answers