TopLink essentials: extra where clause for one to many relationship?

Question

We have a lot of tables that contain "historic" records. Those are marked by a column "historic" holding a value "Y". Sometimes we are not interested in historic values. For example in the next case:
@Entity
@Table(name="ART")
public class Article {
    @OneToMany(mappedBy="article", cascade=CascadeType.ALL, fetch=FetchType.LAZY)
    private Collection<ArticleStats> arcItems;
    public Collection<ArticleStats> getArticleStats() {
        return arcItems;
}One article can have multiple "stats". We are in this case only interested in the "stats" of this article that are not historic. In SQL terms, I would like to add an extra where clause: "WHERE historic = 'N'".
Of course inheritance (with discriminators) is an option, but I don't prefer that. We have a lot of relationships like this and using inheritance would mean we have to add a lot of extra classes. Is there a way to add an extra where clause to the query that is used to retrieve all the stats records related tot my Article?
We use TopLink essentials with an IBM AS/400 database.

Answer 1

The JPA Spec does not handle this case, but TopLink Essentials does. You will need to customize your TopLink descriptor using a DescriptorCustomizer. You can set your DescriptorCustomizer in your persistence.xml using the "toplink.descriptor.customizer.<entity-name>" property set to the class name "<package>.<class>" of your customizer class.
The customizer would look something like:
public class MyCustomizer implements DescriptorCustomizer {
public void customize(ClassDescriptor descriptor) {
OneToManyMapping mapping = (OneToManyMapping )descriptor.getMappingForAttributeName("arcItems");
ExpressionBuilder builder = new ExpressionBuilder();
mapping.setSelectionCriteria(builder.getField("STAT.ART_ID").equal(builder.getParameter("ART.ID").and(builder.getField("HISTORY").equal("N")));
If you never wanted historical records you could also add this expression to your descriptor's additionalJoinExpression.
James Sutherland