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
|
