Hibernate Projections
In this section, you will learn about the hibernate
projections with an appropriate example.
Projections: The package Criteria is used as a
framework by the applications just to build the new kinds of projection. may be used
by applications as a framework for building new kinds of Projection. In
general Projection means to retrieve while in case of SQL Projection means
"Select" clause. Most of the applications uses the built-in
projection types by means of the static factory methods of this class.
Product.java
package net.roseindia;
public class Product {
private int id;
private String name;
private double price;
private Dealer dealer;
private int did;
public Product(String name, double price) {
super();
// TODO Auto-generated constructor stub
this.name = name;
this.price = price;
}
public Product() {
super();
// TODO Auto-generated constructor stub
}
public Dealer getDealer() {
return dealer;
}
public void setDealer(Dealer dealer) {
this.dealer = dealer;
}
public double getDid() {
return did;
}
public void setDid(int did) {
this.did = did;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
}
|
ProjectionList: is the list of projection
instances which are result of Query's object.
Criteria API: enables us to specify criteria
based on various.
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 create a projectionList object add the
fields having properties "name" and "price". Set
it to the Criteria object by invoking the setProjection() method and passing the
projectList object into this method and then add this object into the List
interface's list object and iterate this object list object to display the data
contained in this object.
projectionExample.java
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.ProjectionList;
import org.hibernate.criterion.Projections;
public class projectionExample {
/**
* @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);
ProjectionList proList = Projections.projectionList();
proList.add(Projections.property("name"));
proList.add(Projections.property("price"));
crit.setProjection(proList);
List list = crit.list();
Iterator it = list.iterator();
if(!it.hasNext()){
System.out.println("No any data!");
}
else{
while(it.hasNext()){
Object[] row = (Object[])it.next();
for(int i = 0; i < row.length;i++){
System.out.print(row[i]);
System.out.println();
}
}
}
sess.close();
}
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 this_.name as y0_, this_.price as y1_ from Product
this_
Product Name Price
Computer
23000.0
Mobile
15000.0
Laptop
200.0
Keyboard
1500.0
PenDrive
200.0
HardDisk 2500.0
Computer
100.0 |
|
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Current Comments
1 comments so far (post your own) View All Comments Latest 10 Comments:Thanking your tutorials and servise
Posted by Harsha on Friday, 04.4.08 @ 10:46am | #55287