Re: [eclipselink-users] Problem persisting an inheritance tree

[James Sutherland <jamesssss@xxxxxxxxx>]

EclipseLink does support inheritance in Embeddables, but JPA does not.

Try removing the @MappedSuperclass, and perhaps add an @Inheritance and add
an @DiscriminatorColumn for the Embeddable.  This might not work through
annotations, (please log a bug if it does not), if it does not work you can
define the Embeddable inheritance using a DescriptorCustomizer and setting
the parentClass on the Embeddables InheritancePolicy.

See,
http://en.wikibooks.org/wiki/Java_Persistence/Embeddables#Inheritance

Otherwise change your object model to either add the additional fields in
the Entity instead of the Embeddable, or only define the embeddable in each
subclass.



alaiseca wrote:
> 
> Hi, I have a problem trying to map an inheritance tree. A simplified
> version of my model is like this:
> 
> @MappedSuperclass
> @Embeddable
> public class BaseEmbedded implements Serializable {
> 
>    @Column(name="BE_FIELD")
>    private String beField;
>    
>    // Getters and setters follow
> }
> 
> @MappedSuperclass
> @Embeddable
> public class DerivedEmbedded extends BaseEmbedded {
> 
>   @Column(name="DE_FIELD")
>    private String deField;
>    
>    // Getters and setters follow
> }
> 
> @MappedSuperclass
> public abstract class BaseClass implements Serializable {
> 
>    @Embedded
>    protected BaseEmbedded embedded;
> 
>     public BaseClass() {
>       this.embedded = new BaseEmbedded();
>     }
> 
>      // Getters and setters follow    
> }
> 
> @Entity
> @Table(name="MYTABLE")
> @Inheritance(strategy=InheritanceType.SINGLE_TABLE)
> @DiscriminatorColumn(name="TYPE",
> discriminatorType=DiscriminatorType.STRING)
> public class DerivedClass extends BaseClass {
> 
>     @Id
>     @Column(name="ID", nullable=false)
>     private Long id;
> 
>     @Column(name="TYPE", nullable=false, insertable=false,
> updatable=false)
>     private String type;
> 
>     public DerivedClass() {
>         this.embedded = new DerivedClass();
>     }
> 
>     // Getters and setters follow
> }
> 
> @Entity
> @DiscriminatorValue("A")
> public class DerivedClassA extends DerivedClass {
> 
>     @Embeddable
>     public static NestedClassA extends DerivedEmbedded {
>           
>             @Column(name="FIELD_CLASS_A")
>             private String fieldClassA;
>     }
> 
>     public DerivedClassA() {
>         this.embedded = new NestedClassA();
>     }
> 
>     // Getters and setters follow
> }
> 
> @Entity
> @DiscriminatorValue("B")
> public class DerivedClassB extends DerivedClass {
> 
>     @Embeddable
>     public static NestedClassB extends DerivedEmbedded {
>           
>             @Column(name="FIELD_CLASS_B")
>             private String fieldClassB;
>     }
> 
>     public DerivedClassB() {
>         this.embedded = new NestedClassB();
>     }
> 
>     // Getters and setters follow
> }
> 
> At Java level, this model is working fine, and I believe is the
> appropriate one. My problem comes up when it's time to persist an object. 
> 
> At runtime, I can create an object which could be an instance of
> DerivedClass, DerivedClassA or DerivedClassB. As you can see, each one of
> the derived classes introduces a new field which only makes sense for that
> specific derived class. All the classes share the same physical table in
> the database. If I persist an object of type DerivedClass, I expect fields
> BE_FIELD, DE_FIELD, ID and TYPE to be persisted with their values and the
> remaining fields to be null. If I persist an object of type DerivedClass
> A, I expect those same fields plus the FIELD_CLASS_A field to be persisted
> with their values and field FIELD_CLASS_B to be null. Something equivalent
> for an object of type DerivedClassB. 
> 
> Since the @Embedded annotation is at the BaseClass only, EclipseLink is
> only persisting the fields up to that level in the tree. I don't know how
> to tell EclipseLink that I want to persist up to the appropriate level in
> the tree, depending on the actual type of the embedded property.
> 
> I cannot have another @Embedded property in the subclasses since this
> would duplicate data that is already present in the superclass and would
> also break the Java model. 
> 
> I cannot declare the embedded property to be of a more specific type
> either, since it's only at runtime when the actual object is created and I
> don't have a single branch in the hierarchy. 
> 
> Is it possible to solve my problem? Or should I resignate myself to accept
> that there is no way to persist the Java model as it is? 
> 
> Any help will be greatly appreciated. Thanks
> 
> 


-----
http://wiki.eclipse.org/User:James.sutherland.oracle.com James Sutherland 
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