Question

I have a model, that each class extends Entity:

@MappedSuperclass
public abstract class Entity implements Serializable {
    private Long id;
    .
    .
    .
}

Now, in my model, each Entity could have an attribute:

@javax.persistence.Entity
public class Attribute extends Entity {
    private Entity entity;
    private String name;
    private String value;
    .
    .
    .
}

My question is: How can I map entity attribute of class Attribute ? My idea is to store this attribute as entityClass and entityId, but still I don’t know how to achieve this with JPA?

---

Example of concrete class that extends Entity:

@javax.persistence.Entity
public class Ball extends Entity {
    private Set<Attribute> attributes;

    @OneToMany(cascade = CascadeType.ALL, mappedBy = "entity")
    public Set<Attribute> getAttributes() {
        return attributes;
    }

    public void setAttributes(Set<Attribute> attributes) {
        this.attributes = attributes;
    }
}

Answer 1

There is no easy way to do this in JPA. You could map the relationship as @Transient and add tow @Basic mappings for the id and class (perhaps using property get/set method). Then execute the query in you model code.

If you are using EclipseLink you may be able to use a @VariableOneToOne,

See,

http://www.eclipse.org/eclipselink/documentation/2.4/jpa/extensions/a_variableonetoone.htm#CHDDFDGF