A real parent - child relationship

brama11 · **Joined:** Wed Feb 20, 2008 2:56 pm **Posts:** 1

Hi,

My question is about a real parent - child relationship, where a child has two parents, a mother and a father, and those parents has a collection of children. Both child and parent are of the same class - User. So it's references to the same class, one user is the parent, a father or a mother, to another User.

I am confused about how to do the mapping since I have two many-to-one mappings:

<many-to-one name="father" column="father_id"/>

<many-to-one name="mother" column="mother_id"/>

... that I want to map to the same one-to-many set:

<set name="children" inverse="true">
<key column="?"/>
<one-to-many class="User"/>
</set>

I want the set of children to include users that reference the parent trough both father_id and mother_id.

One way around this problem is as I see it to skip the one-to-many part and just manually collect all the children with HQL query, but that must not be the best way to treat this issue is it?

/Marcus

sjhyam · **Joined:** Fri Jun 01, 2007 12:41 pm **Posts:** 121

Here is my solution:

Basically father, mother and child are of type Person. So Person class has all common properties. Then create Family class that has associations with Father, Mother and Children.

Code:

package com.shyam.model;

/**
 * @hibernate.class
 * @author mutchaS
 *
 */
public class Person {
   private Long id;
   private String name;
   
   public Person() {}
   
   /**
    * @hibernate.id generator-class="native"
    * @return
    */
   public Long getId() {
      return id;
   }
   public void setId(Long id) {
      this.id = id;
   }
   
   /**
    * @hibernate.property
    */
   public String getName() {
      return name;
   }
   public void setName(String name) {
      this.name = name;
   }
}

Code:

package com.shyam.model;

import java.util.Set;

/**
 * @hibernate.class
 * @author mutchaS
 *
 */
public class Family {
   private Long id;
   private Person father;
   private Person mother;
   private Set children;
   
   public Family() {}
   
   /**
    * @hibernate.id generator-class="native"
    * @return
    */
   public Long getId() {
      return id;
   }
   public void setId(Long id) {
      this.id = id;
   }
   
   /**
    * @hibernate.many-to-one not-null="true" cascade="save-update" lazy="false" 
    * @return
    */
   public Person getFather() {
      return father;
   }
   public void setFather(Person father) {
      this.father = father;
   }

   /**
    * @hibernate.many-to-one not-null="true" cascade="save-update" lazy="false"
    * @return
    */
   public Person getMother() {
      return mother;
   }
   public void setMother(Person mother) {
      this.mother = mother;
   }

   
   /**
    * @hibernate.set cascade="save-update, delete, delete-orphan"
    * @hibernate.one-to-many class="com.shyam.model.Child"
    * @hibernate.key column="FAMILY_ID" not-null="true" foreign-key="FK_FAMILY_ID"
    * @hibernate.list-index column="CHILD_POSITION" base="1"
    * @return
    */
   public Set getChildren() {
      return children;
   }
   public void setChildren(Set children) {
      this.children = children;
   }
   
   
}

Code:

package com.shyam.model;

/**
 * @hibernate.joined-subclass
 * @hibernate.joined-subclass-key column="id"
 * @author mutchaS
 *
 */
public class Child extends Person {/*
   private Family family;
   
   *//**
    * @hibernate.many-to-one not-null="true" cascade="save-update" lazy="false"
    * @return
    *//*
   public Family getFamily() {
      return family;
   }

   public void setFamily(Family family) {
      this.family = family;
   }*/
   
   
}

Here is the Person.hbm.cfg

Code:

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping

>

    <class
            name="com.shyam.model.Person"
    >

    <id
        name="id"
            column="id"
    >

    <!-- The generator-class attribute of @hibernate.id is deprecated, use the @hibernate.generator tag instead -->
    <generator class="native">

    </generator>

    </id>

        <property
            name="name"
                    column="name"
        >

        </property>

    <joined-subclass
        name="com.shyam.model.Child"
    >

            <!-- @hibernate.joined-subclass-key tag is deprecated, use @hibernate.key instead -->
            <key
                    column="id"
            />

    </joined-subclass>

    </class>    

</hibernate-mapping>

Here is the Family.hbm.cfg

Code:

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping

>

    <class
            name="com.shyam.model.Family"
    >

    <id
        name="id"
            column="id"
    >

    <!-- The generator-class attribute of @hibernate.id is deprecated, use the @hibernate.generator tag instead -->
    <generator class="native">

    </generator>

    </id>

        <many-to-one
            name="father"
                not-null="true"
                cascade="save-update"
                lazy="false"
        >

        </many-to-one>

        <many-to-one
            name="mother"
                not-null="true"
                cascade="save-update"
                lazy="false"
        >

        </many-to-one>

        <set
            name="children"
            cascade="save-update, delete, delete-orphan"
        >

            <key
                column="FAMILY_ID"
                foreign-key="FK_FAMILY_ID"
                not-null="true"
            >

            </key>          

            <one-to-many
                class="com.shyam.model.Child"
            />

        </set>

    </class>    

</hibernate-mapping>

Here is how I save the family
/

Code:

/First unit of work
      Session session = HibernateUtil.getSessionFactory().openSession();
      Transaction tx = session.beginTransaction();
      
      Person father = new Person();
      father.setName("father1");
      
      Person mother = new Person();
      mother.setName("mother1");
      
      Family family = new Family();
      family.setFather(father);
      family.setMother(mother);
      
      Set children = new HashSet();      
      Child child = new Child();
      child.setName("child1");
      children.add(child);
      
      Child child2 = new Child();
      child2.setName("child2");
      children.add(child2);
      
      family.setChildren(children);
      //session.save(family);
      
      tx.commit();
      session.close();

read family

Code:

List list = (List)session.createCriteria(Family.class).list();
      System.out.println("family: "+list.size());
      for(Iterator it = list.iterator(); it.hasNext();){
         family = (Family)it.next();
         System.out.println("\nfather: "+family.getFather().getName());
         System.out.println("mother: "+family.getMother().getName());
         children = family.getChildren();
         for(Iterator it2 = children.iterator(); it2.hasNext();){
            Child ch = (Child)it2.next();
            System.out.println("children: "+ch.getName());
         }
      }

and find family where

Code:

list = (List)session.createCriteria(Family.class)
               .createAlias("father", "father")
               .add(Restrictions.ilike("father.name", "father1", MatchMode.START))
               .list();
      System.out.println("family: "+list.size());
      for(Iterator it = list.iterator(); it.hasNext();){
         family = (Family)it.next();
         System.out.println("\nfather: "+family.getFather().getName());
         System.out.println("mother: "+family.getMother().getName());
         children = family.getChildren();
         for(Iterator it2 = children.iterator(); it2.hasNext();){
            Child ch = (Child)it2.next();
            System.out.println("children: "+ch.getName());
         }
      }

You can insert inverse relation between Child and Family.

[/code]

anirudhvyas010 · **Joined:** Thu Dec 13, 2007 2:32 pm **Posts:** 26

Have a User class with User field in it and a Set of Users in it.

Something like :

Code:

private User user;
private Set<User> users;

now, for some SQL, just to get you an idea as to what i am talking about ...

Code:

create table  user(user_id number primary key, parent_id number, user_name varchar2(25));

alter table user add constraint fk_parent_id_1 foreign key(parent_id) references user(user_id);

Now for the user mapping ( just a hint though, you can use Reverse engg in mapping but i like to do it by hand all the time ) :

Code:

<class name="User" table="user">
   <id name="userId" column="user_id">
       <generator class="native" />
   </id>
   
   <many-to-one class="User" column="parent_id" />

   <set name="users">
      <key column="user_id" />
      <one-to-many class="User" />
  </set>

</class>

Now understand that parent_id can be null to determine the complete lineage. ( since root cannot have a parent , if you get the picture)