Creating a Ternary Relation -1

In the previous post we saw how to manage a many to many relation with join data. The same concept can be extended further to create a simple ternary relation. In the earlier example  the "shopName" attribute of the join table was a simple String. This could be changed to a Shop Entity instead.
A diagrammatic representation of the relation would be something similar to the below pic:

The Entities in the example would now be

public class Chocolate {
    private Integer id;
    private String name;
    private String brand;
    
    @Override
    public int hashCode() {
        int hash = this.getName().hashCode();
        hash = hash * 17 + this.getBrand().hashCode();
        return hash;
    }

    @Override
    public boolean equals(Object obj) {
        boolean isEqual = false;
        if (obj instanceof Chocolate) {
            Chocolate chocolate = (Chocolate) obj;
            isEqual = chocolate.getName().equals(this.getName())
                    && chocolate.getBrand().equals(this.getBrand());
        }
        return isEqual;
    }
      //setter-getter methods
}

public class Shop {
    private Integer id;
    private String name;
    private String shopCode;
    
    @Override
    public int hashCode() {
        int hash = this.getName().hashCode();
        hash = hash * 17 + this.getShopCode().hashCode();
        return hash;
    }

    @Override
    public boolean equals(Object obj) {
        boolean isEqual = false;
        if (obj instanceof Shop) {
            Shop otherShop = (Shop) obj;
            isEqual = otherShop.getShopCode().equals(this.getShopCode());
        }
        return isEqual;
    }
      //setter-getter methods
}

The people class which includes the details of the ternary relation is :

public class People {
    private Integer id;
    private String name;
    private Set<FirstTrialInfo> favouriteChocolateDetails = new HashSet<FirstTrialInfo>();

    public synchronized void addChocolates(final Chocolate chocolate,
            Date firstTryDate, Shop shop) {
        final FirstTrialInfo firstTrialInfo = new FirstTrialInfo();
        firstTrialInfo.setChocolate(chocolate);
        firstTrialInfo.setFirstTaste(firstTryDate);
        firstTrialInfo.setShop(shop);
        firstTrialInfo.setPeople(this);
        this.getFavouriteChocolateDetails().add(firstTrialInfo);
    }

    public synchronized void removeChocolateFromShop(final Chocolate chocolate, final Shop shop) {
        FirstTrialInfo firstTrialInfo = new FirstTrialInfo();
        firstTrialInfo.setChocolate(chocolate);
        firstTrialInfo.setShop(shop);
        firstTrialInfo.setPeople(this);
        this.getFavouriteChocolateDetails().remove(firstTrialInfo);
    }

    @Override
    public int hashCode() {
        int hash = this.getName().hashCode();
        return hash;
    }

    @Override
    public boolean equals(Object obj) {
        boolean isEqual = false;
        if (obj instanceof People) {
            People people = (People) obj;
            isEqual = people.getName().equals(this.getName());
        }
        return isEqual;
    }
    //setter-getter methods
}

The FirstTrialInfo class acts as the component here.

public class FirstTrialInfo {
    private People people;
    private Chocolate chocolate;
    private Shop shop;
    private Date firstTaste;
    
    @Override
    public boolean equals(Object obj) {
        boolean isEqual = false;
        if (obj instanceof FirstTrialInfo) {
            FirstTrialInfo firstTrialInfo = (FirstTrialInfo) obj;
            isEqual = firstTrialInfo.getChocolate().equals(this.getChocolate())
                    && firstTrialInfo.getShop().equals(this.getShop())
                    && firstTrialInfo.getPeople().equals(this.getPeople());
        }
        return isEqual;
    }

    @Override
    public int hashCode() {
        int hash = this.getChocolate().hashCode();
        hash = hash * 17 + this.getPeople().hashCode();
        hash = hash * 41 + this.getShop().hashCode();
        return hash;
    }

    //setter-getter methods
}

The hibernate mappings for the entities is as below:
Chocolate.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.association.ternary.component">
    <class name="Chocolate" table="CHOCOLATE">
        <id name="id" type="integer">
            <column name="ID" />
            <generator class="identity" />
        </id>
        <property name="name" type="string">
            <column name="NAME" />
        </property>
            <property name="brand" type="string">
            <column name="BRAND" />
        </property>

    </class>
</hibernate-mapping>

Shop.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.association.ternary.component">
    <class name="Shop" table="SHOP">
        <id name="id" type="integer">
            <column name="ID" />
            <generator class="identity" />
        </id>
        <property name="name" type="string">
            <column name="NAME" />
        </property>

        <property name="shopCode" type="string">
            <column name="SHOP_CODE" unique="true"/>
        </property>

    </class>
</hibernate-mapping>

The People.hbm.xml file provides details of the ternary association.

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.association.ternary.component">
    <class name="People" table="PEOPLE">
        <id name="id" type="integer">
            <column name="ID" />
            <generator class="identity" />
        </id>
        <property name="name" type="string">
            <column name="NAME" />
        </property>

        <set name="favouriteChocolateDetails" table="CHOCOLATE_FAN">
            <key column="FAN_ID" foreign-key="CHOCOLATE_FAN_FK1" />
            <composite-element class="FirstTrialInfo">
                <parent name="people" />
                <many-to-one name="chocolate" class="Chocolate" column="CHOCOLATE_ID"
                    foreign-key="CHOCOLATE_FAN_FK2" not-null="true" />
                <many-to-one name="shop" class="Shop" column="SHOP_ID"
                    foreign-key="CHOCOLATE_FAN_FK3" not-null="true" />
                <property name="firstTaste" type="timestamp">
                    <column name="FIRST_TASTE_DATE" not-null="true" />
                </property>
            </composite-element>
        </set>
    </class>
</hibernate-mapping>

The tables created by Hibernate on startup is :

create table CHOCOLATE (
        ID integer not null auto_increment,
        NAME varchar(255),
        BRAND varchar(255),
        primary key (ID)
    )
    create table CHOCOLATE_FAN (
        FAN_ID integer not null,
        CHOCOLATE_ID integer not null,
        SHOP_ID integer not null,
        FIRST_TASTE_DATE datetime not null,
        primary key (FAN_ID, CHOCOLATE_ID, SHOP_ID, FIRST_TASTE_DATE)
    )
    create table PEOPLE (
        ID integer not null auto_increment,
        NAME varchar(255),
        primary key (ID)
    )
    create table SHOP (
        ID integer not null auto_increment,
        NAME varchar(255),
        SHOP_CODE varchar(255) unique,
        primary key (ID)
    )
    alter table CHOCOLATE_FAN 
        add index CHOCOLATE_FAN_FK3 (SHOP_ID), 
        add constraint CHOCOLATE_FAN_FK3 
        foreign key (SHOP_ID) 
        references SHOP (ID)
    alter table CHOCOLATE_FAN 
        add index CHOCOLATE_FAN_FK1 (FAN_ID), 
        add constraint CHOCOLATE_FAN_FK1 
        foreign key (FAN_ID) 
        references PEOPLE (ID)
    alter table CHOCOLATE_FAN 
        add index CHOCOLATE_FAN_FK2 (CHOCOLATE_ID), 
        add constraint CHOCOLATE_FAN_FK2 
        foreign key (CHOCOLATE_ID) 
        references CHOCOLATE (ID)

The component manages the ternary relation. The code to create one such relation would be as below:

static void create() {
    Chocolate chocolate1 = new Chocolate();
    chocolate1.setName("Eclairs");
    chocolate1.setBrand("Cadburys");
    Chocolate chocolate2 = new Chocolate();
    chocolate2.setName("Melody");
    chocolate2.setBrand("Parles");

    Shop shop = new Shop();
    shop.setName("Chocolate Factory");
    shop.setShopCode("#4555");

    People people1 = new People();
    people1.setName("Naina");
    people1.addChocolates(chocolate1, new Date(), shop);

    Session session = sessionFactory.openSession();
    Transaction t = session.beginTransaction();
    session.save(chocolate1);
    session.save(shop);
    session.save(people1);
    session.save(chocolate2);//no association to any entity
    t.commit();
    System.out.println("The Person with name " + people1.getName()
            + " was created with id " + people1.getId());
    System.out.println("Chocolate1 saved with id " + chocolate1.getId()
            + " for shop " + shop.getName()
            + " and Chocolate2 saved with id " + chocolate2.getId());
}

The logs indicate successful creation:

3157 [main] DEBUG org.hibernate.SQL  - 
    insert 
    into
        CHOCOLATE
        (NAME, BRAND) 
    values
        (?, ?)
...
3344 [main] DEBUG org.hibernate.SQL  - 
    insert 
    into
        SHOP
        (NAME, SHOP_CODE) 
    values
        (?, ?)
...
3438 [main] DEBUG org.hibernate.SQL  - 
    insert 
    into
        PEOPLE
        (NAME) 
    values
        (?)
...
3438 [main] DEBUG org.hibernate.SQL  - 
    insert 
    into
        CHOCOLATE
        (NAME, BRAND) 
    values
        (?, ?)
...
3516 [main] DEBUG org.hibernate.SQL  - 
    insert 
    into
        CHOCOLATE_FAN
        (FAN_ID, CHOCOLATE_ID, SHOP_ID, FIRST_TASTE_DATE) 
    values
        (?, ?, ?, ?)
The Person with name Naina was created with id 1
Chocolate1 saved with id 1 for shop Chocolate Factory and Chocolate2 saved with 
id 2