Cyclic relationships in Hibernate -

i want map tree in hibernate, persisting results in exception because of cyclic reference (the relationships not bidirectional).

class node {     @manytoone     node parent;      @onetoone     node leftchild;      @onetoone     node rightchild; } 

node n references left child l in turn references n again parent. also, node n references right child r in turn again references n again parent. however, cannot make relationships bidirectional, because parent inverse of both leftchild , rightchild. best way make model persistable?

regards, jochen

i don't see problem:

@entity class node {     @id @generatedvalue     private int id;     private string name;      @manytoone(cascade = cascadetype.all)     node parent;      @onetoone(cascade = cascadetype.all)     node leftchild;      @onetoone(cascade = cascadetype.all)     node rightchild;      node() {}      public node(string name) {         this.name = name;     }     // omitted getters , setters brevity }  public static void main(string[] args) {     sessionfactory sessionfactory = new configuration()                   .addannotatedclass(node.class)                   .setproperty("hibernate.connection.url",                       "jdbc:h2:mem:foo;db_close_delay=-1")                   .setproperty("hibernate.hbm2ddl.auto", "create")                   .buildsessionfactory();     session session = sessionfactory.opensession();     transaction transaction = session.begintransaction();     node = new node("a");     node b = new node("b");     node c = new node("c");     node d = new node("d");     node e = new node("e");     a.setleftchild(b);     b.setparent(a);     a.setrightchild(c);     c.setparent(a);     b.setleftchild(d);     d.setparent(b);     b.setrightchild(e);     e.setparent(b);     system.out.println("before saving:");     print(a, 1);     serializable rootnodeid = session.save(a);     transaction.commit();     session.close();      session = sessionfactory.opensession();     node root = (node) session.load(node.class, rootnodeid);     system.out.println("freshly loaded:");     print(root, 1);     session.close(); }  private static void print(node node, int depth) {     if (node == null) { return; }     system.out.format("%" + depth + "s\n", node);     print(node.getleftchild(), depth + 1);     print(node.getrightchild(), depth + 1); }