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Hibernate Projection Count

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In this section, you will learn to hibernate projection count. The example demonstrates the rowCount() method of the projection interface.

Hibernate Projection Count

     

In this section, you will learn to hibernate projection count. The example demonstrates the rowCount() method of the projection interface.

A unidirectional one-to-many association on a foreign key is rarely required.

<?xml version="1.0" encoding="UTF-8"?>

 <!DOCTYPE hibernate-mapping
 PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"
 "http://hibernate.sourceforge.net
   /hibernate-mapping-3.0.dtd"
>

<hibernate-mapping>
 <class name="net.roseindia.Dealer">
  <id name="id" type="int">
 <generator class="increment"/>
  </id>

  <property name="name" type="string"/>
  <bag name="product" inverse="true" 
   cascade=
"all,delete-orphan">
  <key column="did"/>
  <one-to-many class="net.roseindia.Product"/>
  </bag>

 </class>
</hibernate-mapping>

A unidirectional one-to-many association on a foreign key is rarely required.

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-mapping
 PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"
 "http://hibernate.sourceforge.net
  /hibernate-mapping-3.0.dtd"
>

<hibernate-mapping>
 <class name="net.roseindia.Product">
  <id name="id" type="int">
 <generator class="increment"/>
  </id>

  <property name="name" type="string"/>
  <property name="did" type="int"/>
  <property name="price" type="double"/>
  <many-to-one name="dealer" class=
  "net.roseindia.Dealer" column="did" 
  insert=
"false" update="false"/>

 </class>
 
</hibernate-mapping>

Here is the hibernate code:

In the class projectionExample.java,  first we create the session object with the help of the SessionFactory interface. Then we use the createQuery() method of the Session object which returns a Query object. Now we use the openSession() method of the SessionFactory interface simply to instantiate the Session object.

Then we obtain the criteria object simply by invoking the createCriteria() method of the Session's object. Now we set the number of rows count simply by calling the setProjection() method of the Criteria APIs and passing it the rowCount() method of the Projections interface. Then pass the reference of the Criteria object into the List interface object and finally iterate this object to count the number of rows.

package net.roseindia;

import java.util.Iterator;
import java.util.List;

import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.criterion.Projection;
import org.hibernate.criterion.Projections;
import org.hibernate.criterion.Restrictions;

public class projectionCount {

  /**
 @param args
 */
  public static void main(String[] args) {
  // TODO Auto-generated method stub
  
  Session sess = null;
  try {
  SessionFactory sfact = new 
  Configuration
().configure().buildSessionFactory();
  sess = sfact.openSession();
  Criteria crit = sess.createCriteria(Product.class);
  crit.setProjection(Projections.rowCount());
  List list = crit.list();
  Iterator it = list.iterator();
  if (!it.hasNext()){
  System.out.println("No any data!");
  }
  else{
  while(it.hasNext()){
  Object count = it.next();
  System.out.println("Row: " + count);  
  }
  }
  
  }
  catch(Exception e){
  System.out.println(e.getMessage());
  }

  }

}

Output:

log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).

log4j:WARN Please initialize the log4j system properly.

Hibernate: select count(*) as y0_ from Product this_

Row: 7

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Posted on: March 10, 2008

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Comments:1
Lelala Lelala
July 22, 2012
Thanks for the hin to "ProjectionCount" !

Thanks for the hint to use Projections & Count, this is much faster than the old way of doing List().Count() :-) Thanks a lot!
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