JPA : Master-Detail template with extended classes and deserialization

Hi have two entities: one for the master (a document)

@Inheritance(strategy = InheritanceType.JOINED)
public class DocumentStandard implements Serializable {

    private static final long serialVersionUID = -712220124306015698L;

    @Column(name = "number")
    private Integer number;

    ...
}

and one for the rows

@Inheritance(strategy = InheritanceType.JOINED)
public class RowStandard<D extends DocumentStandard> implements Serializable {

    private static final long serialVersionUID = -8343803021263172062L;

    @JoinColumn(name = "iddoc", nullable = false)
    @ManyToOne(targetEntity = DocumentStandard.class, fetch = FetchType.EAGER)
    private D doc;
    ...

}

These are my template classes. I extend these classes for particular documents:

• DocA extends DocumentStandard

• RowA extends RowStandard

There is a way to specify that doc in rowA is of type DocA ?

Why I need this detail?

Because I've a json deserializer (jackson) that use java reflection for sanitarizing my data, for instance change all enums received as object 'enum' :{ 'text': 'Open', 'value':'O'} in 'enum':'O'.

I do it reading all fields that are entities, for example in RowA i find doc of type DocumentStandard. So, I search for enums in the DocumentStandard class and correct the relative json. But if the enum is in DocA, i don't find it.

How can i get with reflection the real type of doc field?