@Entity
public class SampleGroup implements TreeNode {
    @Id @GeneratedValue
    private Long id;
   
    @ManyToOne(optional=true)
    private SampleGroup myParent;
   
    @OneToMany(mappedBy="myParent")
    @Cascade({CascadeType.ALL,CascadeType.DELETE_ORPHAN})
    private Set<SampleGroup> includesGroups = new LinkedHashSet<SampleGroup>();

    @Embedded
    private TreeNodeInfo treeNodeInfo = new TreeNodeInfo();
   
    private String treeName;
   
    private String groupName;
   
   
   
    public SampleGroup() {
        super();
        treeName = " Simple Group ";
    }

    public TreeNodeInfo getNodeInfo() {
        return treeNodeInfo;
    }

    public TreeNode getParent() {
        return myParent;
    }

    public String getTreeName() {
        return treeName;
    }

   
    /**
     * @return the myParent
     */
    public SampleGroup getMyParent() {
        return myParent;
    }

    /**
     * @param myParent the myParent to set
     */
    public void setMyParent(SampleGroup myParent) {
        this.myParent = myParent;
    }

    /**
     * @return the treeNodeInfo
     */
    public TreeNodeInfo getTreeNodeInfo() {
        return treeNodeInfo;
    }

    /**
     * @param treeNodeInfo the treeNodeInfo to set
     */
    public void setTreeNodeInfo(TreeNodeInfo treeNodeInfo) {
        this.treeNodeInfo = treeNodeInfo;
    }

    /**
     * @return the groupName
     */
    public String getGroupName() {
        return groupName;
    }

    /**
     * @param groupName the groupName to set
     */
    public void setGroupName(String groupName) {
        this.groupName = groupName;
    }

    /**
     * @param treeName the treeName to set
     */
    public void setTreeName(String treeName) {
        this.treeName = treeName;
    }

    /**
     * @return the id
     */
    public Long getId() {
        return id;
    }
   
    public void includeGroup(SampleGroup group) {
        group.setMyParent(this);
        includesGroups.add(group);
    }
   
    public void excludeGroup(SampleGroup group) {
        if (this.equals(group.getMyParent())) {
            group.setMyParent(null);
            includesGroups.remove(group);
        }       
    }
   
    public boolean includesGroup(SampleGroup group) {
        return includesGroups.contains(group);
    }
   
    private static MessageFormat messageFormat = new MessageFormat("tree=''{0}'', group=''{1}'', id={2}, {3} ");
   
   
    @Override
    public String toString() {
        return messageFormat.format(new Object[]{treeName,groupName,id,treeNodeInfo});
    }

        SampleGroup group1 = new SampleGroup();
        group1.setGroupName("group 1");
       
        SampleGroup group2 = new SampleGroup();
        group2.setGroupName("group 2");
       
        SampleGroup group3 = new SampleGroup();
        group3.setGroupName("group 3");
       
        group1.includeGroup(group2);
        group2.includeGroup(group3);
        sampleGroupRepository.save(group1);
        assertNotNull(group1.getId());
        assertNotNull(group2.getId());
        assertNotNull(group3.getId());
       
       
        //Flushes the session and clears it.
        flushAndClear();

        SampleGroup _1_reloaded = sampleGroupRepository.findById( group1.getId() );
        SampleGroup _2_reloaded = sampleGroupRepository.findById( group2.getId() );
        SampleGroup _3_reloaded = sampleGroupRepository.findById( group3.getId() );
       
        assertNotNull( _1_reloaded );
        assertNotNull( _2_reloaded );
        assertNotNull( _3_reloaded );
       
        assertTrue( _1_reloaded.includesGroup(_2_reloaded) );
        assertTrue( _2_reloaded.includesGroup(_3_reloaded) );
       
        //Move 3 from 2 to 1.
        _2_reloaded.excludeGroup(_3_reloaded);
        _1_reloaded.includeGroup(_3_reloaded);
       
        assertTrue( _1_reloaded.includesGroup(_2_reloaded) );
        assertTrue( _1_reloaded.includesGroup(_3_reloaded) );
       
        assertFalse( _2_reloaded.includesGroup(_3_reloaded) );

        sampleGroupRepository.update(_1_reloaded);
       
        flushAndClear();
       
        _1_reloaded = sampleGroupRepository.findById( group1.getId() );
        _2_reloaded = sampleGroupRepository.findById( group2.getId() );
        _3_reloaded = sampleGroupRepository.findById( group3.getId() );

        assertNotNull(_3_reloaded);//This fails.
        //assertNotNull(_2_reloaded); //This also fails.