Hibernate One To Many Mapping Example Using Annotation

Previously we have learned about Hibernate One To One Mapping Using annotation. In this Hibernate One To Many mapping Example, we will learn about One To Many mapping between Java objects and database tables using Hibernate framework (Annotation Mapping). 

Creating table

Create AUTHOR and BOOK Tables, simply Copy and Paste the following SQL query in the query editor to get the table created.

CREATE TABLE "AUTHOR" 
( 
 "AUTHOR_ID" NUMBER(10,0) NOT NULL ENABLE,
 "AUTHOR_NAME" VARCHAR2(40 BYTE) NOT NULL ENABLE,
 PRIMARY KEY (AUTHOR_ID)
);

CREATE TABLE "BOOK" 
 ( "BOOK_ID" NUMBER(10,0) NOT NULL ENABLE, 
 "AUTHOR_ID" NUMBER(10,0) NOT NULL ENABLE, 
 "BOOK_TITLE" VARCHAR2(255 CHAR), 
 "BOOK_DESCRIPTION" VARCHAR2(255 CHAR), 
 PRIMARY KEY ("BOOK_ID"),
 CONSTRAINT fk_book FOREIGN KEY("AUTHOR_ID") REFERENCES AUTHOR("AUTHOR_ID")
 );

Folder Structure:

1. Create a simple Maven Project “HibernateTutorial” and create a package for our source files “com.javainterviewpoint” under  src/main/java 
2. Now add the following dependency in the POM.xml

   <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0	http://maven.apache.org/xsd/maven-4.0.0.xsd">
      <modelVersion>4.0.0</modelVersion>
      <groupId>HibernateTutorial</groupId>
      <artifactId>HibernateTutorial</artifactId>
      <version>0.0.1-SNAPSHOT</version>
      <properties>
         <hibernate.version>4.3.11.Final</hibernate.version>
         <oracle.connector.version>11.2.0</oracle.connector.version>
      </properties>
   
      <dependencies>
        <!-- Hibernate -->
        <dependency>
           <groupId>org.hibernate</groupId>
           <artifactId>hibernate-core</artifactId>
           <version>${hibernate.version}</version>
        </dependency>
   
        <!-- Oracle -->
        <dependency>
           <groupId>com.oracle</groupId>
           <artifactId>ojdbc14</artifactId>
           <version>${oracle.connector.version}</version>
        </dependency>
      </dependencies>
      <build>
        <sourceDirectory>src</sourceDirectory>
        <plugins>
          <plugin>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.3</version>
            <configuration>
            <source>1.7</source>
            <target>1.7</target>
            </configuration>
          </plugin>
        </plugins>
      </build>
    </project>

3. Create the Java classes Author.java, Book.java, HibernateOneToMany.java and RetriveAuthorAndBook.java under  com.javainterviewpoint folder.
4. Place the hibernate.cfg.xml under the src/main/resources  directory

Hibernate One To Many Mapping Example

Author.java

Create a new Java file Author.java under the package com.javainterviewpoint and add the following code

package com.javainterviewpoint;

import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
@Table(name="AUTHOR")
public class Author
{
    @Id
    @GeneratedValue
    @Column(name="AUTHOR_ID")
    private int authorId;
    
    @Column(name="AUTHOR_NAME")
    private String authorName;
    
    @OneToMany(mappedBy="author",cascade = CascadeType.ALL)
    private Set<Book> books;
    
    public Author()
    {
        super();
    }

    public Author(int authorId, String authorName, Set books)
    {
        super();
        this.authorId = authorId;
        this.authorName = authorName;
        this.books = books;
    }

    public int getAuthorId()
    {
        return authorId;
    }

    public void setAuthorId(int authorId)
    {
        this.authorId = authorId;
    }

    public String getAuthorName()
    {
        return authorName;
    }

    public void setAuthorName(String authorName)
    {
        this.authorName = authorName;
    }

    public Set<Book> getBooks()
    {
        return books;
    }

    public void setBooks(Set<Book> books)
    {
        this.books = books;
    }

    @Override
    public String toString()
    {
        return "Author [authorId=" + authorId + ", authorName=" + authorName + ", books=" + books + "]";
    }
}

Our Author class is a simple POJO class consisting of the getters and setters for the Author properties (authorId, authorName, books).

In the POJO class, we have used the below JPA Annotations.

1. @Entity – This annotation will mark our Employee class as an Entity Bean.
2. @Table – @Table annotation will map our class to the corresponding database table. You can also specify other attributes such as indexes, catalog, schema, uniqueConstraints. The @Table annotation is an optional annotation if this annotation is not provided then the class name will be used as the table name.
3. @Id –  The @Id annotation marks the particular field as the primary key of the Entity.
4. @GeneratedValue – This annotation is used to specify how the primary key should be generated. Here SEQUENCE Strategy will be used as this the default strategy for Oracle
5. @OneToMany – We have used the mappedBy attribute – This denotes the property which will be used for mapping purpose, here we have an attribute “author” so in our Book class we should have this attribute. This is a mandatory annotation.
6. @Column – This annotation maps the corresponding fields to their respective columns in the database table.

Book.java

Create a new Java file Book.java under the package com.javainterviewpoint and add the following code

package com.javainterviewpoint;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
@Table(name="BOOK")
public class Book
{
    @Id
    @GeneratedValue
    @Column(name="BOOK_ID")
    private int bookId;
    
    @Column(name="BOOK_TITLE")
    private String bookTitle;
    
    @Column(name="BOOK_DESCRIPTION")
    private String bookDescription;
    
    @ManyToOne
    @JoinColumn(name="AUTHOR_ID")
    private Author author;

    public Book()
    {
        super();
    }

    public Book(int bookId, String bookTitle, String bookDescription, Author author)
    {
        super();
        this.bookId = bookId;
        this.bookTitle = bookTitle;
        this.bookDescription = bookDescription;
        this.author = author;
    }

    public int getBookId()
    {
        return bookId;
    }

    public void setBookId(int bookId)
    {
        this.bookId = bookId;
    }

    public String getBookTitle()
    {
        return bookTitle;
    }

    public void setBookTitle(String bookTitle)
    {
        this.bookTitle = bookTitle;
    }

    public String getBookDescription()
    {
        return bookDescription;
    }

    public void setBookDescription(String bookDescription)
    {
        this.bookDescription = bookDescription;
    }

    public Author getAuthor()
    {
        return author;
    }

    public void setAuthor(Author author)
    {
        this.author = author;
    }

    @Override
    public String toString()
    {
        return "Book [bookId=" + bookId + ", bookTitle=" + bookTitle + ", bookDescription=" + bookDescription
                + ", author=" + author + "]";
    }
}

@ManyToOne annotation defines the relationship many to one (One Author can have many Book)

@JoinColumn annotation indicates that this entity will act as the owner of the relationship (This table has a column with a foreign key to the referenced table)

hibernate.cfg.xml

Place the hibernate.cfg.xml file also under the src/main/resources folder

 <?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>

 <!-- Database connection settings -->
 <property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
 <property name="hibernate.connection.username">root</property>
 <property name="hibernate.connection.password">root</property>
 <property name="hibernate.connection.url">jdbc:oracle:thin:@mydb:40051:dev</property>

 <!-- JDBC connection pool (use the built-in) -->
 <property name="connection.pool_size">1</property>

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

 <!-- Echo all executed SQL to stdout -->
 <property name="show_sql">true</property>

 <!-- Drop and re-create the database schema on startup -->
 <property name="hibernate.hbm2ddl.auto">update</property>

 <!-- Mapping classes -->
 <mapping class="com.javainterviewpoint.Author" />
 <mapping class="com.javainterviewpoint.Book" />
</session-factory> 
</hibernate-configuration>

• First and foremost property is for specifying the JDBC Driver class, in my case it OracleDriver

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

• Give the connection URL for connecting the database and provide username and password for connecting the above database

<property name="hibernate.connection.url">jdbc:oracle:thin:@mydb:40051:dev</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.connection.password">root</property>

• Specify the connection pool size, this property limits the number of connections in the Hibernate connection pool.

<property name="connection.pool_size">1</property>

• Dialect Property makes the Hibernate generate the SQL for the corresponding database which is being used. In this example we are using Oracle database hence Oracle query will be generated. If you are using MySQL database then you need to change the dialect accordingly.

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

• The show_sql property will print the executed sql in the console when set to true.

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

• If the property “hibernate.hbm2ddl.auto” is set to “create”  This will drop and recreate the database schema on every execution. If it is set to “update” then the database schema will be updated every time rather than dropping and recreating.

<property name="hibernate.hbm2ddl.auto">update</property>

• Under the Mapping class tag  we need to specify all the mapping file for which we need the table to be created or updated.

<mapping class="com.javainterviewpoint.Author" />
<mapping class="com.javainterviewpoint.Book" />

HibernateOneToMany.java

package com.javainterviewpoint;

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

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;

public class HibernateOneToMany
{
    public static void main(String args[])
    {
        //Reading the hibernate configuration file
        Configuration configuration = new Configuration().configure("hibernate.cfg.xml");
        StandardServiceRegistryBuilder regBuilber = new StandardServiceRegistryBuilder();
        regBuilber.applySettings(configuration.getProperties());
        ServiceRegistry serviceRegistry = regBuilber.build();
        
        //Create SessionFacctory
        SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);
        
        //Create Session from SessionFactory
        Session session = sessionFactory.openSession();
        
        //Begin the transaction
        session.beginTransaction();
        
        //Create a new Author Object
        Author author = new Author();
        author.setAuthorName("JavaInterviewPoint");

        //Create a new Book Object        
        Book book1 = new Book();
        book1.setBookTitle("Hibernate");
        book1.setBookDescription("Hibernate Description");
        book1.setAuthor(author);

        //Create a new Book Object        
        Book book2 = new Book();
        book2.setBookTitle("Spring");
        book2.setBookDescription("Spring Description");
        book2.setAuthor(author);
        
        //Adding books to the Set
        Set<Book> books = new HashSet();
        books.add(book1);
        books.add(book2);
        author.setBooks(books);
       
        session.save(author);
             
        //Commit the changes
        session.getTransaction().commit();
        //Close the session
        session.close();
    }
}

• Create the Configuration object and read the configuration file using the configure() method.

Configuration configuration = new Configuration().configure("hibernate.cfg.xml");

• Get the SessionFactory object through the buildSessionFactory() method of the configuration object.

SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);

• openSession() method opens up the new session and begin a new transaction

Session session = sessionFactory.openSession();
session.beginTransaction();

• Create a new Author object and set values to its properties

Author author = new Author();
author.setAuthorName("JavaInterviewPoint");

• Create two Book objects (book1, book2) and set value to it properties

Book book1 = new Book();
book1.setBookTitle("Hibernate");
book1.setBookDescription("Hibernate Description");
book1.setAuthor(author);

Book book2 = new Book();
book2.setBookTitle("Spring");
book2.setBookDescription("Spring Description");
book2.setAuthor(author);

• Create a Set and add book1 and book2 to and set it books property of Author class

Set<Book> books = new HashSet();
books.add(book1);
books.add(book2);
author.setBooks(books);

• save() method of the session object will persist the author object into the database. It in-turn saves book1 and book2 as we have given CascadeType.ALL

session.save(author);

• Finally get the transaction and commit the changes and close the session.

session.getTransaction().commit();
session.close();

Console:

INFO: HHH000261: Table found: AUTHOR
Dec 26, 2016 12:29:35 PM org.hibernate.tool.hbm2ddl.TableMetadata <init>
INFO: HHH000037: Columns: [author_name, author_id]
Dec 26, 2016 12:29:35 PM org.hibernate.tool.hbm2ddl.TableMetadata <init>
INFO: HHH000108: Foreign keys: []
Dec 26, 2016 12:29:35 PM org.hibernate.tool.hbm2ddl.TableMetadata <init>
INFO: HHH000126: Indexes: [sys_c0014856]
Dec 26, 2016 12:29:38 PM org.hibernate.tool.hbm2ddl.TableMetadata <init>
INFO: HHH000261: Table found: BOOK
Dec 26, 2016 12:29:38 PM org.hibernate.tool.hbm2ddl.TableMetadata <init>
INFO: HHH000037: Columns: [book_description, book_title, book_id, author_id]
Dec 26, 2016 12:29:38 PM org.hibernate.tool.hbm2ddl.TableMetadata <init>
INFO: HHH000108: Foreign keys: [fk_book]
Dec 26, 2016 12:29:38 PM org.hibernate.tool.hbm2ddl.TableMetadata <init>
INFO: HHH000126: Indexes: [sys_c0014859]
Dec 26, 2016 12:29:38 PM org.hibernate.tool.hbm2ddl.SchemaUpdate execute
INFO: HHH000232: Schema update complete
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: insert into AUTHOR (AUTHOR_NAME, AUTHOR_ID) values (?, ?)
Hibernate: insert into BOOK (AUTHOR_ID, BOOK_DESCRIPTION, BOOK_TITLE, BOOK_ID) values (?, ?, ?, ?)
Hibernate: insert into BOOK (AUTHOR_ID, BOOK_DESCRIPTION, BOOK_TITLE, BOOK_ID) values (?, ?, ?, ?)

RetriveAuthorAndBook.java

package com.javainterviewpoint;

import java.util.List;
import java.util.Set;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;

public class RetriveAuthorAndBook
{
    public static void main(String args[])
    {
        //Reading the hibernate configuration file
        Configuration configuration = new Configuration().configure("hibernate.cfg.xml");
        StandardServiceRegistryBuilder regBuilber = new StandardServiceRegistryBuilder();
        regBuilber.applySettings(configuration.getProperties());
        ServiceRegistry serviceRegistry = regBuilber.build();
        
        //Create SessionFacctory
        SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);
        
        //Create Session from SessionFactory
        Session session = sessionFactory.openSession();
        
        List<Author> authorList = session.createQuery("from Author").list();
        for(Author author : authorList)
        {
            System.out.println("** Author Details **");
            System.out.println("Author Id   : "+ author.getAuthorId());
            System.out.println("Author Name : "+ author.getAuthorName());
            
            System.out.println("** Book Details **");
            Set<Book> books = author.getBooks();
            for(Book book : books)
            {
                System.out.println("Book Id   : "+book.getBookId());
                System.out.println("Book Name : "+book.getBookTitle());
                System.out.println("Book Name : "+book.getBookDescription());
                System.out.println("");
            }
        }
        //Close the session
        session.close();
    }
}

Output:

Hibernate: select author0_.AUTHOR_ID as AUTHOR_ID1_0_, author0_.AUTHOR_NAME as AUTHOR_NAME2_0_ from AUTHOR author0_
** Author Details **
Author Id : 270
Author Name : JavaInterviewPoint
** Book Details **
Hibernate: select books0_.AUTHOR_ID as AUTHOR_ID4_0_0_, books0_.BOOK_ID as BOOK_ID1_1_0_, books0_.BOOK_ID as BOOK_ID1_1_1_, books0_.AUTHOR_ID as AUTHOR_ID4_1_1_, books0_.BOOK_DESCRIPTION as BOOK_DESCRIPTION2_1_1_, books0_.BOOK_TITLE as BOOK_TITLE3_1_1_ from BOOK books0_ where books0_.AUTHOR_ID=?
Book Id : 271
Book Name : Hibernate
Book Name : Hibernate Description

Book Id : 272
Book Name : Spring
Book Name : Spring Description