Using Hibernate to generate id incrementally

As we have seen in the last section that the increment class generates identifiers of type long, short or int that are unique only when no other process is inserting data into the same table. In this lesson I will show you how to write running program to demonstrate it. You should not use this method to generate the primary key in case of clustured environment.

In this we will create a new table in database, add mappings in the contact.hbm.xml file, develop the POJO class (Book.java), write the program to test it out.

Create Table in the mysql database:
User the following sql statement to create a new table in the database.

CREATE TABLE `book` (
`id` int(11) NOT NULL default '0',
`bookname` varchar(50) default NULL,
PRIMARY KEY (`id`)
) TYPE=MyISAM

Developing POJO Class (Book.java)
Book.java is our POJO class which is to be persisted to the database table "book".




public class Book {
private long lngBookId;
private String strBookName;

/**
* @return Returns the lngBookId.
*/
public long getLngBookId() {
return lngBookId;
}
/**
* @param lngBookId The lngBookId to set.
*/
public void setLngBookId(long lngBookId) {
this.lngBookId = lngBookId;
}
/**
* @return Returns the strBookName.
*/
public String getStrBookName() {
return strBookName;
}
/**
* @param strBookName The strBookName to set.
*/
public void setStrBookName(String strBookName) {
this.strBookName = strBookName;
}
}

Adding Mapping entries to contact.hbm.xml
Add the following mapping code into the contact.hbm.xml file

<class name="roseindia.tutorial.hibernate.Book" table="book">
<id name="lngBookId" type="long" column="id" >
<generator class="increment"/>
</id>

<property name="strBookName">
<column name="bookname" />
</property>
</class>

Note that we have used increment for the generator class. *After adding the entries to the xml file copy it to the bin directory of your hibernate eclipse project(this step is required if you are using eclipse).

Write the client program and test it out
Here is the code of our client program to test the application.


//Hibernate Imports
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;


public class IdIncrementExample {
public static void main(String[] args) {
Session session = null;

try{
// This step will read hibernate.cfg.xml and prepare hibernate for use
SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
session =sessionFactory.openSession();

org.hibernate.Transaction tx = session.beginTransaction();

//Create new instance of Contact and set values in it by reading them from form object
System.out.println("Inserting Book object into database..");
Book book = new Book();
book.setStrBookName("Hibernate Tutorial");
session.save(book);
System.out.println("Book object persisted to the database.");
tx.commit();
session.flush();
session.close();
}catch(Exception e){
System.out.println(e.getMessage());
}finally{
}

}
}

To test the program Select Run->Run As -> Java Application from the eclipse menu bar. This will create a new record into the book table.