How to map entity with JPA? - jpa-2.0

Question

I can't get the right mapping for the field tree in this class:
#Entity
#Table(name = "SushiMapTree")
public class SushiMapTree<K, V> extends Persistable implements Map<K,V> {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name="SushiMapID")
protected int ID;
#OneToOne(cascade = CascadeType.ALL)
#JoinTable(name="SushiMapTree_SushiTree")
private SushiTree<SushiMapElement<K, V>> tree = new SushiTree<SushiMapElement<K,V>>();
This are the other classes and their mappings:
#Entity
#Table(name = "SushiTree")
public class SushiTree<T> extends Persistable implements Collection<T> {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name="SushiTreeID")
protected int ID;
#Column(name="Test")
private String test = "Test";
#OneToMany(cascade = CascadeType.PERSIST)
#JoinTable(name="SushiTree_SushiTreeElements")
private List<SushiTreeElement<T>> treeElements = new ArrayList<SushiTreeElement<T>>();
#OneToMany(cascade = CascadeType.PERSIST)
#JoinTable(name="SushiTree_SushiTreeRootElements")
private List<SushiTreeElement<T>> treeRootElements = new ArrayList<SushiTreeElement<T>>();
}
#Entity
#Table(name = "SushiMapElement")
public class SushiMapElement<K, V> extends Persistable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int ID;
#ManyToOne(cascade = CascadeType.PERSIST)
private SushiMapElement<K, V> parent;
#OneToMany(cascade = CascadeType.PERSIST)
private List<SushiMapElement<K, V>> children = new ArrayList<SushiMapElement<K, V>>();
#Column(name = "MapKey")
K key;
#Column(name = "MapValue")
V value;
The other classes work well, but I can't get the right mapping. I tried different mappings for some hours with Column, JoinColumn, JoinTable and so on. Eclipse Link does not create the database and says to use a ValueHolderInterface:
The attribute [tree] is not declared as type ValueHolderInterface, but its mapping uses indirection.
Thanks for your help!

Answer 1

I solved the problem with the following annotation:
#ManyToOne(cascade=CascadeType.PERSIST)
#JoinColumn(name="TreeID")
But I don't know, why it work this way.