Is it possible to have discriminator column on secondary table in jpa

Question

I'm currently struggling with mapping an existing db schema to jpa entities, and among a lot of weirdness, I've become stuck on this problem.

I have two tables, similar to this:

Table 1          Table 2         
|Service     |  |Servicetype     |
|servicetype |  |Servicecategory |
|            |  |                |

Where servicetype in table 1 is a foreign key to service type in table two. However, the services in table 1 have wildly different behaviour based on which category they belong to (while there are 100+ servicetypes, there are only 4 categories) I'd like to be able to be a able to map table 1 to four different entityclasses, based on the category of their service type.

This is what I have so far:

@Entity
@Table(name = "table1")
@DiscriminatorColumn(name = "servicecategory", discriminatorType =         
     discriminatorType.INTEGER)
@DiscriminatorValue("1")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@SecondaryTable(name = "table2",
pkJoinColumns =
 @PrimaryKeyJoinColumn(name = "servicetype", referencedColumnName = 
"servicetype"))
public class AbstractService implements Serializable {
...etc

And 4 classes extending from this, buth with a different discriminatorvalue , Which doesn't work, since eclipselink, which I'm using, tries to lookup the value of servicecategory in table1.

Is it possible to express such a mapping with jpa or should I just do the mapping with " where servicecategory = ? " on each query.

Answer 1

Please file an enhancement in EclipseLink to add support for this feature. A JPA solution would be to switch the primary table with the secondary table - this might cause problems with insertion order though and foreign keys will be referencing the Servicetype in table2.

An EclipseLink specific solution is to use a customizer to change the table used for the descriminator field. Add the @Customizer tag to the entity and specify a class with a method:

public void customize(ClassDescriptor descriptor) {
    descriptor.getInheritancePolicy().getClassIndicatorField().setTable(
        descriptor.getTable("table2"));
}