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Example of @Formula in Hibernate Annotation

By Arvind Rai, February 01, 2013
Hibernate Annotation has some property annotation that provides different type of job. If we want to apply a virtual property in your entity to get a calculated value, we can use @Formula annotation to set the formula. This formula can be as complex as we want. In the example we are showing area of a Dimension entity.
Dimension.java
package com.concretepage.persistence;
import java.io.Serializable;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;
import org.hibernate.annotations.Formula;

@Entity
@Table(name="dimension")
public class Dimension implements Serializable {
	
	private static final long serialVersionUID = 1L;

	@Id
	@Column(name="id")
	private int id;
	
	@Column(name="length")
	private int length;
	
	@Column(name="width") 
	private int width;
	
	@Formula(" length * width ")
	public long area;
	
	public Dimension(int id,int length, int width){
		this.id=id;
		this.length=length;
		this.width=width;
	}

	public long getArea() {
		return area;
	}

	public void setArea(long area) {
		this.area = area;
	}

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public int getLength() {
		return length;
	}

	public void setLength(int length) {
		this.length = length;
	}

	public int getWidth() {
		return width;
	}

	public void setWidth(int width) {
		this.width = width;
	}
}
 
hibernate.cfg.xml
<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
  <session-factory>
    <property name="hibernate.connection.url">
    jdbc:mysql://localhost:3306/hibernate</property>
    <property name="hibernate.connection.username">root</property>
    <property name="hibernate.connection.password"></property>
    <property name="hibernate.connection.pool_size">10</property>
    <property name="show_sql">true</property>
    <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
    <property name="hibernate.hbm2ddl.auto">update</property>
       
    <mapping class="com.concretepage.persistence.Dimension"/>
 
   </session-factory>
</hibernate-configuration>
 
HibernateUtil.java
package com.concretepage.util;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
import com.concretepage.persistence.Dimension;

public class HibernateUtil {
	private static final SessionFactory concreteSessionFactory;
	    static {
	        try {
	            concreteSessionFactory = new AnnotationConfiguration()
	                    .configure().buildSessionFactory();
	        } catch (Throwable ex) {
	            throw new ExceptionInInitializerError(ex);
	        }
	    }
	    public static Session getSession()
	            throws HibernateException {
	        return concreteSessionFactory.openSession();
	    }
	    
	    public static void main(String... args){
	    	Session session=getSession();
	    	session.beginTransaction();
	    	Dimension d1 = new Dimension(1,2,5);
	    	session.save(d1);
	    	Dimension d2 = new Dimension(2,3,4);
	    	session.save(d2);
	    	session.getTransaction().commit();
	    	session.refresh(d1);
	    	session.refresh(d2);
	        Dimension d=  (Dimension)session.get(Dimension.class,new Integer(1));	
	        
	        System.out.println(d.getArea());
	    }
	}
 
Output
Hibernate: insert into dimension (length, width, id) values (?, ?, ?)
Hibernate: insert into dimension (length, width, id) values (?, ?, ?)
Hibernate: select dimension0_.id as id0_0_, dimension0_.length as length0_0_, dimension0_.width as width0_0_,  dimension0_.length * dimension0_.width  as formula0_0_ from dimension dimension0_ where dimension0_.id=?
Hibernate: select dimension0_.id as id0_0_, dimension0_.length as length0_0_, dimension0_.width as width0_0_,  dimension0_.length * dimension0_.width  as formula0_0_ from dimension dimension0_ where dimension0_.id=?
10
 
POSTED BY
ARVIND RAI
ARVIND RAI
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