<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.linuslan.model">
    <class name="Category" table="CATEGORIES">
        <id name="id" column="ID">
            <generator class="sequence">
                <param name="sequence">CATEGORIES_SEQ</param>
            </generator>
        </id>
        <property name="name" column="NAME"></property>
        <many-to-one name="parentCategory" column="CATEGORY_ID" class="com.linuslan.model.Category" cascade="save-update" lazy="false"></many-to-one>
        <set name="childCategories" table="CATEGORIES" inverse="true" cascade="all-delete-orphan">
            <key column="CATEGORY_ID"></key>
            <one-to-many class="com.linuslan.model.Category"/>
        </set>
    </class>
</hibernate-mapping>

package com.linuslan.model;

import java.util.HashSet;
import java.util.Set;

public class Category {
    private Long id;
    private String name;
    private Category parentCategory;
    private Set<Category> childCategories = new HashSet<Category>();
    
    public Category() {
    }

    public Category(String name, Set<Category> childCategories, Category parentCategory) {
       this.name = name;
       this.childCategories = childCategories;
       this.parentCategory = parentCategory;
    }
    
    public Long getId() {
        return id;
    }
    @SuppressWarnings("unused")
    private void setId(Long id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Category getParentCategory() {
        return parentCategory;
    }
    public void setParentCategory(Category parentCategory) {
        this.parentCategory = parentCategory;
    }
    public Set<Category> getChildCategories() {
        return childCategories;
    }
    public void setChildCategories(Set<Category> childCategories) {
        this.childCategories = childCategories;
    }
    
}

package com.linuslan.business;

import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;


import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;

import com.linuslan.model.Category;
import com.linuslan.util.HibernateUtil;

public class CategoryBusinessService {
        public void saveParentCategory() {
        Category food = new Category();
        food.setName("food");
        Category fruit = new Category();
        fruit.setName("fruit");
        Category vegetable = new Category();
        vegetable.setName("vegetable");
        Set<Category> secondChildCategories = new HashSet<Category>();
        secondChildCategories.add(fruit);
        secondChildCategories.add(vegetable);
        food.setChildCategories(secondChildCategories);
        
        Session session = this.sessionFactory.openSession();