code: public ForeignKey<OneToMany<T>> getOrCreateMapKeyForeignKey()
     {
        Node node = childNode.getOrCreate("map-key-foreign-key");
        ForeignKey<OneToMany<T>> mapKeyForeignKey = new ForeignKeyImpl<OneToMany<T>>(this, "map-key-foreign-key", childNode, node);
        return mapKeyForeignKey;
     }
docs: If not already created, a new <code>map-key-foreign-key</code> element with the given value will be created.
  Otherwise, the existing <code>map-key-foreign-key</code> element will be returned.
  @return  a new or existing instance of <code>ForeignKey<OneToMany<T>></code>