Bidirectional One-To-One Relationship with Join Tables in Hibernate

In bidirectional association, we will have navigation in both direction, i.e, both side of the association will have the reference to the other side. The both side of the association will implement one of the collection interfaces, if it has the reference to the other entity.

In one to one relationship, one source object can have relationship with only one target object. Let’s consider CD and Artist. So one CD can be written by one Artist or an Artist can write only one CD. So we will create two tables CD and Artist in the database and we will see how one-to-one relationship works step by step.

Now we will apply one-to-one relationship. So only one CD can be written by only one Artist.

A bidirectional one-to-one association on a join table is possible, but extremely unusual.

Step 1. Create tables

Create table – cd

CREATE TABLE `cd` (
  `cdId` bigint(20) NOT NULL AUTO_INCREMENT,
  `cdTitle` varchar(50) NOT NULL,
  PRIMARY KEY (`cdId`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=latin1;

 

Create table – artist

CREATE TABLE `artist` (
  `artistId` bigint(20) NOT NULL AUTO_INCREMENT,
  `artistName` varchar(50) NOT NULL,
  PRIMARY KEY (`artistId`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=latin1;

 

Create table – cdartist

CREATE TABLE `cdartist` (
  `artistId` bigint(20) NOT NULL,
  `cdId` bigint(20) NOT NULL,
  PRIMARY KEY (`cdId`),
  UNIQUE KEY `artistId` (`artistId`),
  UNIQUE KEY `cdId` (`cdId`),
  KEY `FK82065EE860AB4868` (`cdId`),
  KEY `FK82065EE835296F34` (`artistId`),
  CONSTRAINT `FK82065EE835296F34` FOREIGN KEY (`artistId`) REFERENCES `artist` (`artistId`),
  CONSTRAINT `FK82065EE860AB4868` FOREIGN KEY (`cdId`) REFERENCES `cd` (`cdId`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

 

Step 2. Create a java project in any Java based IDE and configure for hibernate jars.

Step 3. Create hibernate reverse engineering and configuration file.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-reverse-engineering PUBLIC "-//Hibernate/Hibernate Reverse Engineering DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-reverse-engineering-3.0.dtd">
<hibernate-reverse-engineering>
  <schema-selection match-catalog="hibernate_assoc"/>
  <table-filter match-name="cd"/>
  <table-filter match-name="artist"/>
</hibernate-reverse-engineering>

 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
  <session-factory>
    <!-- hibernate database specific dialect -->
    <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
    <!-- hibernate database specific driver -->
    <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
    <!-- hibernate database connection URL -->
    <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/hibernate_assoc?zeroDateTimeBehavior=convertToNull</property>
    <!-- hibernate database username -->
    <property name="hibernate.connection.username">root</property>
    <!-- show sql in console -->
    <property name="hibernate.show_sql">true</property>
    <!-- format sql in cosole for better readability -->
    <property name="hibernate.format_sql">true</property>
    <!-- which context to use for sql processing -->
    <property name="hibernate.current_session_context_class">thread</property>
    <!-- translator for HSQL -->
    <property name="hibernate.query.factory_class">org.hibernate.hql.classic.ClassicQueryTranslatorFactory</property>
    <!-- hibernate mapping resources or files -->
    <mapping resource="in/webtuts/hibernate/domain/Artist.hbm.xml"/>
    <mapping resource="in/webtuts/hibernate/domain/Cd.hbm.xml"/>
  </session-factory>
</hibernate-configuration>

 

Step 4. Create hibernate utility class which creates singleton SessionFactory from which Session object will be created.

package in.webtuts.hibernate.utils;
 
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.SessionFactory;
 
/**
 * Hibernate Utility class with a convenient method to get Session Factory
 * object.
 *
 * @author admin
 */
public class HibernateUtil {
 
    private static final SessionFactory sessionFactory;
 
    static {
        try {
            // Create the SessionFactory from standard (hibernate.cfg.xml)
            // config file.
            sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
        } catch (Throwable ex) {
            // Log the exception.
            System.err.println("Initial SessionFactory creation failed." + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }
 
    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
}

 

Step 5. Create mapping xml file and POJO for artist table. Look at the xml file, we have <many-to-one /> with constraint unique=”true” inside <join/> which makes sure that one-to-one relationship with join tables and only one CD can be written by one Artist.

<?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>
    <class name="in.webtuts.hibernate.domain.Artist" table="artist" catalog="hibernate_assoc">
        <id name="artistId" type="java.lang.Long">
            <column name="artistId" />
            <generator class="identity" />
        </id>
        <property name="artistName" type="string">
            <column name="artistName" length="50" not-null="true" />
        </property>
        <join table="cdartist" inverse="true" optional="true">
            <key column="artistId" unique="true"/>
            <many-to-one name="cd" column="cdId" not-null="true" unique="true" cascade="all"/>
        </join>
    </class>
</hibernate-mapping>
package in.webtuts.hibernate.domain;

public class Artist implements java.io.Serializable {

    private Long artistId;
    private String artistName;
    private Cd cd;

    public Artist() {
    }

    public Long getArtistId() {
        return this.artistId;
    }

    public void setArtistId(Long artistId) {
        this.artistId = artistId;
    }

    public String getArtistName() {
        return this.artistName;
    }

    public void setArtistName(String artistName) {
        this.artistName = artistName;
    }

    public Cd getCd() {
        return cd;
    }

    public void setCd(Cd cd) {
        this.cd = cd;
    }

}

 

Step 6. Create mapping xml file and POJO for cd table.

<?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>
    <class name="in.webtuts.hibernate.domain.Cd" table="cd" catalog="hibernate_assoc">
        <id name="cdId" type="java.lang.Long">
            <column name="cdId" />
            <generator class="identity" />
        </id>
        <property name="cdTitle" type="string">
            <column name="cdTitle" length="50" not-null="true" />
        </property>        
        <join table="cdartist" optional="true">
            <key column="cdId" unique="true"/>
            <many-to-one name="artist" column="artistId" not-null="true" unique="true" cascade="all"/>
        </join>
    </class>
</hibernate-mapping>

 

package in.webtuts.hibernate.domain;

public class Cd implements java.io.Serializable {

    private Long cdId;
    private String cdTitle;
    private Artist artist;

    public Cd() {
    }

    public Long getCdId() {
        return this.cdId;
    }

    public void setCdId(Long cdId) {
        this.cdId = cdId;
    }

    public String getCdTitle() {
        return this.cdTitle;
    }

    public void setCdTitle(String cdTitle) {
        this.cdTitle = cdTitle;
    }

    public Artist getArtist() {
        return artist;
    }

    public void setArtist(Artist artist) {
        this.artist = artist;
    }

}

 

Step 7. Now we will create a main class for testing one-to-one using join tables.

package in.webtuts.hibernate.test;

import in.webtuts.hibernate.domain.Artist;
import in.webtuts.hibernate.domain.Cd;
import in.webtuts.hibernate.utils.HibernateUtil;
import java.io.Serializable;
import org.hibernate.Session;
import org.hibernate.Transaction;

/**
 *
 * @author https://www.jeejava.com
 */
public class OneToOneBidirectionalJoin {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        Session session = null;
        Transaction transaction = null;
        try {
            session = HibernateUtil.getSessionFactory().getCurrentSession();
            transaction = session.beginTransaction();

            Artist a = new Artist();
            a.setArtistName("abc");

            Cd cd = new Cd();
            cd.setCdTitle("Java");

            cd.setArtist(a);

            Serializable cdId = session.save(cd);

            Cd loadCd = (Cd) session.load(Cd.class, cdId);
            System.out.println("Cd ID: " + loadCd.getCdId());
            System.out.println("Cd Title: " + loadCd.getCdTitle());
            System.out.println("Artist ID: " + loadCd.getArtist().getArtistId());
            System.out.println("Artist Name: " + loadCd.getArtist().getArtistName());

            transaction.commit();
        } catch (Exception e) {
            e.printStackTrace();
            transaction.rollback();
        }
    }

}

 

Step 8. Run the main class and see the output as shown below. While we save value for artist, the below values are stored into the database tables.

inserted data into artist table

insert  into `artist`(`artistId`,`artistName`) values (1,'abc');

inserted data into cd table

insert  into `cd`(`cdId`,`cdTitle`) values (1,'Java');

inserted data into cdartist table

insert  into `cdartist`(`artistId`,`cdId`) values (1,1);

Console Output

Hibernate:
    insert
    into
        hibernate_assoc.artist
        (artistName)
    values
        (?)
Hibernate:
    insert
    into
        hibernate_assoc.cd
        (cdTitle)
    values
        (?)
Hibernate:
    insert
    into
        cdartist
        (artistId, cdId)
    values
        (?, ?)
Cd ID: 1
Cd Title: Java
Artist ID: 1
Artist Name: abc

That’s all. Thanks for your reading.

Soumitra Roy Sarkar

I am a professional Web developer, Enterprise Application developer, Software Engineer and Blogger. Connect me on Roy Tutorials Twitter Facebook  Google Plus Linkedin

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