EDIT

@Entity

@Audited

public class PolytomousKeyNode extends VersionableEntity implements IMultiLanguageTextHolder {

	private static final Logger logger = LogManager.getLogger(PolytomousKeyNode.class);

	// This is the main key a node belongs to. Although other keys may also

	@XmlSchemaType(name = "IDREF")

	@Cascade({ CascadeType.SAVE_UPDATE, CascadeType.MERGE })

	@ManyToOne(fetch = FetchType.LAZY, targetEntity = PolytomousKeyNode.class)

	private PolytomousKeyNode parent;

	//see comment on children @IndexColumn

		}

		if(nodeNumber == null) {

        }

		children.add(index, child);

		} else {

			node.setNodeNumber(nodeN);

			newNodeN++;

			for (PolytomousKeyNode child : children) {

				if (node == child){

					throw new RuntimeException("Parent and child are the same for the given key node. This will lead to an infinite loop when updating node numbers.");