Polymorphic association in static metamodel JPA

Question

I have an entity which contain polymorphic association to few entities. It definition:

@Entity
@Table(name = "notifications")
public class Notification implements java.io.Serializable {

//some fields ...

//Polymorphic association
@Any (metaColumn = @Column(name = "target_type"), fetch = FetchType.LAZY)
@AnyMetaDef(idType = "integer", metaType = "string",
        metaValues = {
        @MetaValue(targetEntity = Task.class, value = "Task"),
        @MetaValue(targetEntity = AdminNote.class, value = "AdminNote"),
        @MetaValue(targetEntity = UserCancelRequest.class, value = "UserCancelRequest"),
        //@MetaValue(targetEntity = TransferInfo.class, value = "TransferInfo"),
        //@MetaValue(targetEntity = NoteSubscription.class, value = "NoteSubscription")
})
@JoinColumn(name = "target_id")
@Getter
@Setter
private NotificationAssociation target;

My polymorphic association represented by interface NotificationAssociation:

public interface NotificationAssociation {
/**
 * Return actual type of associated entity
 * @return one of {@link NotificationTargetType}
 */
String getTargetType();

/**
 * Return associated entity id. Used in queries
 * @return target entity id
 */
Integer getTargetId();
}

And this works. But i need an access to target from Notification class in criteria though static metamodel API. My metamodel:

@StaticMetamodel(Notification.class)
public class Notification_ {
public static volatile SingularAttribute<Notification, Integer> id;
public static volatile SingularAttribute<Notification, Integer>   postedById;
public static volatile SingularAttribute<Notification, Integer> adminId;
public static volatile SingularAttribute<Notification, NotificationAssociation> target;
public static volatile SingularAttribute<Notification, Date> hiddenAt;
public static volatile SingularAttribute<Notification, Date> createdAt;

}

In HQL/JPQL i can get access to it, but in metamodel target is null, and when i get model trough Root#getModel() a target isn't present in attributes list. And my question is can i do so or there is any other solution. Thanks for your help

Answer 1

I'm pretty sure you solved your problem but I recently faced the same issue. And on my case I really needed to use CriteriaAPI since I had some generic processing for creating specifications. Since HQL was not an option for me and we cannot mix HQL with specifications. I fixed this issue by mapping the column twice. Using your example:

@Any (metaColumn = @Column(name = "target_type"), fetch = FetchType.LAZY)
@AnyMetaDef(idType = "integer", metaType = "string",
        metaValues = {
        @MetaValue(targetEntity = Task.class, value = "Task"),
        @MetaValue(targetEntity = AdminNote.class, value = "AdminNote"),
        @MetaValue(targetEntity = UserCancelRequest.class, value = "UserCancelRequest")
})
@JoinColumn(name = "target_id")
@Getter
@Setter
private NotificationAssociation target;

@Column(name = "target_id", insertable = false, updatable = false)
private Integer targetId;

Doing that small tweak the metadata gets generated for targetId field and it becomes available on Criteria API. So then you can do something like:

notificationService.getAll((root, query, cb) -> cb.and(cb.equals(root.get("targetId"), someId), ...))

I hope this helps to anybody that is facing the same issue.

Answer 2

Think I figure it out. An @Any annotation and related to it (@AnyMetadef and other) provides by Hibernate, not JPA. So we can't use JPA Criteria API to manage this kind of relations, but we can use Hibernate Criteria API instead.