@Entity
@Access(value = AccessType.FIELD)
@Table(name = "map_owner")
public class MapOwner implements Identifiable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @ElementCollection(fetch = FetchType.EAGER)
    @CollectionTable(name = "map_owner_values", joinColumns = @JoinColumn(name = "owner", nullable = false, insertable = true, updatable = false))
    @Fetch(FetchMode.JOIN)
    @ForeignKey(name = "fk_map_owner")
    private Map<Key, ValueObject> map = new HashMap<Key, ValueObject>();

    public Long getId() {

        return this.id;
    }

    public Map<Key, ValueObject> getMap() {

        return this.map;
    }
}

@Embeddable
@Access(AccessType.FIELD)
public class Key implements Comparable<Key> {

    @Column(name = "key_id")
    private Integer id;

    @Column(name = "key_name")
    private String name;

    public Key() {

        // for hibernate
    }

    public Key(Integer traderId, String articleNo) {

        this.id = traderId;
        this.name = articleNo;
    }


    @Column(name = "key_id", nullable = false, updatable = false)
    public Integer getId() {

        return id;
    }

    @Column(name = "key_name", nullable = false, updatable = false)
    public String getName() {

        return name;
    }
   
    // compareTo, equals and hashCode omitted

}

@Embeddable
@Access(AccessType.FIELD)
public class ValueObject {

    @Transient
    private Key key;

    @Column(name = "value")
    private Double value;

    public ValueObject() {

        // Hibernate
    }

    public ValueObject(Integer keyId, String keyName, Double value) {

        this(new Key(keyId, keyName), value);
    }

    public ValueObject(Key key, Double value) {

        this.key = key;
        this.value = value;
    }

    public Key getKey() {

        return this.key;
    }

    public Double getValue() {

        return this.value;
    }
}