Hibernate One-to-One mapping with Annotations with JoinColumn

Hibernate One-to-One mapping with Annotations with JoinColumn:

This Hibernate tutorial demonstrates how to use JPA annotations in order to implement a unidirectional one-to-one association on a foreign key.

@JoinColumn : The annotation @JoinColumn indicates that this entity is the owner of the relationship (that is: the corresponding table has a column with a foreign key to the referenced table)

We are going to develop a sample Hibernate application using the following technologies/software programs:
1.    Hibernate 4.2.6.Final
2.    JDK 7
3.    Eclipse IDE
4.    Oracle database

Note that we use the latest stuffs to date, you can use little bit lower or higher versions. Now, let’s following the steps below:
    Table of content:
1.    Creating Database and Tables
2.    Creating Eclipse Project
3.    Coding Model Classes with Annotations
4.    Writing Hibernate Configuration File
5.    Writing a Test Program

1. Creating Database and Tables

Execute the following SQL script to create  two tables author and book:

CREATE TABLE AUTHOR (

  AUTHOR_ID NUMBER(11) NOT NULL,

  NAME VARCHAR2(45),

  EMAIL VARCHAR2(45),

  PRIMARY KEY (AUTHOR_ID)

);

CREATE TABLE BOOK (

  BOOK_ID NUMBER(11) NOT NULL,

  TITLE VARCHAR(128),

  DESCRIPTION VARCHAR(512),

  PUBLISHED DATE,

  AUTHOR_ID NUMBER(11),

  PRIMARY KEY (BOOK_ID),

  CONSTRAINT AUTHOR_FK FOREIGN KEY (AUTHOR_ID) REFERENCES AUTHOR (AUTHOR_ID)

);

          COMMIT;

2. Creating Eclipse Project:

The project consists of the following files:

Model classes: Author.java and Book.java

Hibernate XML configuration file: hibernate.cfg.xml

Test program: BooksManager.java

Create a project in Eclipse with the following structure:
             
                                            

3. Coding Model Classes with Annotations:


The followings are code of the two model classes: Author.java and Book.java.

Author.java

package com.hibernate.practice.onetoone;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import javax.persistence.Table;

@Entity

@Table(name="AUTHOR")

public class Author {

       private Long authorId;

       private String name;

       private String email;

      

       public Author(){

             }

       public Author(String name, String email) {

        this.name = name;

        this.email = email;

    }

       @Id

       @Column(name="AUTHOR_ID")

       @GeneratedValue

       public Long getAuthorId() {

             return authorId;

       }

       public void setAuthorId(Long authorId) {

             this.authorId = authorId;

       }

       @Column(name="NAME")

       public String getName() {

             return name;

       }

       public void setName(String name) {

             this.name = name;

       }

       @Column(name="EMAIL")

       public String getEmail() {

             return email;

       }

       public void setEmail(String email) {

             this.email = email;

       }

}

Book.java

 package com.hibernate.practice.onetoone;

import java.util.Date;

import javax.persistence.CascadeType;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.OneToOne;

import javax.persistence.Table;

import javax.persistence.Temporal;

import javax.persistence.TemporalType;

@Entity

@Table(name="BOOK")

public class Book {

       private Long bookId;

       private String bookTitle;

       private String bookDescription;

       private Date publishedDate;

      

       private Author author;

      

       public Book(){

            

       }

       @Id

       @Column(name="BOOK_ID")

       @GeneratedValue

       public Long getBookId() {

             return bookId;

       }

       public void setBookId(Long bookId) {

             this.bookId = bookId;

       }

      

       @Column(name="TITLE")

       public String getBookTitle() {

             return bookTitle;

       }

       public void setBookTitle(String bookTitle) {

             this.bookTitle = bookTitle;

       }

      

       @Column(name="DESCRIPTION")

       public String getBookDescription() {

             return bookDescription;

       }

       public void setBookDescription(String bookDescription) {

             this.bookDescription = bookDescription;

       }

       @Temporal(TemporalType.DATE)

       @Column(name="PUBLISHED")

       public Date getPublishedDate() {

             return publishedDate;

       }

       public void setPublishedDate(Date publishedDate) {

             this.publishedDate = publishedDate;

       }

      

       @OneToOne(cascade = CascadeType.ALL)

       @JoinColumn(name="AUTHOR_ID")

       public Author getAuthor() {

             return author;

       }

       public void setAuthor(Author author) {

             this.author = author;

       }

}

 As you notice, we use the following JPA annotations:

·       @Entity: is required for every model class.

·       @Table: maps the class with the corresponding database table. If omitted, Hibernate will use the class name.

·       @Column: maps the field with the corresponding table column. If omitted, Hibernate will infer the column name and type based on signatures of the getter/setter.

·       @Id and @GeneratedValue: are used in conjunction for a field that maps to the primary key. The values for this field are auto generated.

·       @Temporal: must be used with a java.util.Date field to specify the actual SQL type of the column.

·       @OneToOne and @JoinColumn: are used together to specify a one-to-one association and the join column.

4. Writing Hibernate Configuration File

Write XML configuration for database settings and mapping classes in the hibernate.cfg.xml file as follows:

hibernate.cfg.xml 

<?xml version='1.0' encoding='utf-8'?>

<!DOCTYPE hibernate-configuration PUBLIC

        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"

        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>      

 <session-factory>

  <property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>

  <property name="hibernate.connection.url">jdbc:oracle:thin:@127.0.0.1:1521:orcl</property>

  <property name="hibernate.connection.username">PRACTICE</property>

  <property name="hibernate.connection.password">PRACTICE</property>

  <property name="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</property>

  <property name="show_sql">true</property>

 

       <!--Mapping Entity Starts -->

    <mapping class="com.hibernate.practice.onetoone.Book"/>

    <mapping class="com.hibernate.practice.onetoone.Author"/>

    <!--Mapping Entity Ends -->

   

</session-factory>

</hibernate-configuration>

5. Writing a Test Program

Write code for the test program (BooksManager.java) as follows:

package com.hibernate.practice.onetoone;

import java.util.Date;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.cfg.Configuration;

import org.hibernate.service.ServiceRegistry;

import org.hibernate.service.ServiceRegistryBuilder;

public class BookManager {

       public static void main(String[] args) {

             // loads configuration and mappings

        Configuration configuration = new Configuration().configure();

        ServiceRegistryBuilder registry = new ServiceRegistryBuilder();

        registry.applySettings(configuration.getProperties());

        ServiceRegistry serviceRegistry = registry.buildServiceRegistry();

       

        // builds a session factory from the service registry

        SessionFactory sessionFactory =  

                      configuration.buildSessionFactory(serviceRegistry);

       

        // obtains the session

        Session session = sessionFactory.openSession();

        session.beginTransaction();

       

     // creates a Book entity

        Book newBook = new Book();

        newBook.setBookTitle("Effective Java");

        newBook.setBookDescription("A Programming Language Guide (Java Series)");

        newBook.setPublishedDate(new Date());

       

        newBook.setAuthor(new Author("Joshua Bloch", "Joshua@gmail.com"));

       

        // persists the book entity

        Long bookId = (Long) session.save(newBook);

        

        // gets the book entity back

        Book book = (Book) session.get(Book.class, bookId);

        System.out.println("Book's Title: " + book.getBookTitle());

        System.out.println("Book's Description: " + book.getBookDescription());

        

        Author author = book.getAuthor();

        System.out.println("Author's Name: " + author.getName());

        System.out.println("Author's Email: " + author.getEmail());

        

        session.getTransaction().commit();

        session.close();    

       }

}

Output of the program:

Hibernate: select hibernate_sequence.nextval from dual

Hibernate: select hibernate_sequence.nextval from dual

Book's Title: Effective Java

Book's Description: A Programming Language Guide (Java Series)

Author's Name: Joshua Bloch

Author's Email: Joshua@gmail.com

Hibernate: insert into AUTHOR (EMAIL, NAME, AUTHOR_ID) values (?, ?, ?)

Hibernate: insert into BOOK (AUTHOR_ID, DESCRIPTION, TITLE, PUBLISHED, BOOK_ID) values (?, ?, ?, ?, ?)

Result in the Book and Author table:

                    

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