code: public MapKeyColumn<ManyToMany<T>> getOrCreateMapKeyColumn()
     {
        Node node = childNode.getOrCreate("map-key-column");
        MapKeyColumn<ManyToMany<T>> mapKeyColumn = new MapKeyColumnImpl<ManyToMany<T>>(this, "map-key-column", childNode, node);
        return mapKeyColumn;
     }
docs: If not already created, a new <code>map-key-column</code> element with the given value will be created.
  Otherwise, the existing <code>map-key-column</code> element will be returned.
  @return  a new or existing instance of <code>MapKeyColumn<ManyToMany<T>></code>