package acme.hibernatetest.entities;

import java.util.*;
import javax.persistence.*;

@Entity
public class Node {

   @Id
   private String name;

   @OneToMany
   private List<Node> children;
   
   Node () {
      // required for JPA
   }
   
   public Node(String name, List<Node> children) {
      this.name = name;
      this.children = new ArrayList<>(children);
   }
      
   public String getName() {
      return name;
   }
   
   public List<Node> getChildren() {
      return children;
   }   
}

package acme.hibernatetest.entities;

import java.util.UUID;

import javax.persistence.*;

@Entity
public class NodeRelation {
   
   @Id
   private String uuid;
   
   @ManyToOne
   private Node ancestor;
   
   @ManyToOne
   private Node descendant;
   
   private int distance;
   
   
   NodeRelation() {
      // required for JPA
   }
   
   public NodeRelation(Node ancestor, Node descendant, int distance) {
      uuid = UUID.randomUUID().toString();
      this.ancestor = ancestor;
      this.descendant = descendant;
      this.distance = distance;
   }

   public String getUuid() {
      return uuid;
   }

   public Node getAncestor() {
      return ancestor;
   }

   public Node getDescendant() {
      return descendant;
   }
   
   public int getDistance() {
      return distance;
   }
   
}

@Test
   public void hhh123Test() throws Exception {
      EntityManager entityManager = entityManagerFactory.createEntityManager();
      
      // prepare data in separate transaction
      entityManager.getTransaction().begin();
      Node leafNode = new Node("Leaf", Collections.emptyList());
      entityManager.persist(leafNode);
      
      Node innerNode = new Node("Inner", Collections.singletonList(leafNode));
      entityManager.persist(innerNode);
      
      Node rootNode = new Node("Root", Collections.singletonList(innerNode));
      entityManager.persist(rootNode);
      
      entityManager.persist(new NodeRelation(rootNode, rootNode, 0));
      entityManager.persist(new NodeRelation(rootNode, innerNode, 1));      
      entityManager.persist(new NodeRelation(rootNode, leafNode, 2));
      entityManager.persist(new NodeRelation(innerNode, innerNode, 0));      
      entityManager.persist(new NodeRelation(innerNode, leafNode, 1));
      entityManager.persist(new NodeRelation(leafNode, leafNode, 0));
      
      entityManager.getTransaction().commit();
      
      // clear all cached entities
      entityManager.clear();      
      
      entityManager.getTransaction().begin();
      
      // we don't care about the result here
      List<NodeRelation> relations =
            entityManager.createQuery("SELECT nr FROM NodeRelation AS nr LEFT JOIN FETCH nr.descendant d LEFT JOIN FETCH d.children", NodeRelation.class).getResultList();

      // of interest is the Node with id "Inner" which has incorrectly 2 children (two times the same object)
      Node n = entityManager.find(Node.class, "Inner");      
      Assert.assertNotNull(n);
      Assert.assertEquals(1, n.getChildren().size());
      
      entityManager.getTransaction().rollback();
      entityManager.close();
   }