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Hibernate: Criteria Queries in Depth


HQL forces programmers to drop into an SQL-like syntax for certain operations. So it would seem that Hibernate developers still need to know SQL. Fortunately, Hibernate offers a set of APIs that map the SQL functionality to objects. This allows programmers to use an entirely object-oriented approach without falling back on a relational methodology. Keep reading to find out more.

Author Info:
By: A.P.Rajshekhar
Rating: 4 stars4 stars4 stars4 stars4 stars / 155
March 15, 2006
TABLE OF CONTENTS:
  1. · Hibernate: Criteria Queries in Depth
  2. · The Core Classes of Criteria Queries
  3. · Using Criteria Queries
  4. · A Criteria Query in the Real World

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Hibernate: Criteria Queries in Depth - A Criteria Query in the Real World
(Page 4 of 4 )

Now it is time to apply what we have discussed up till now. In this section I will be rewriting the application developed in the previous article (HQL in Depth). Almost all the code is same except the query part. So the details are as below:

package com.someorg.persist.op;

import java.util.List;

import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import com.someorg.persist.Order
import org.hibernate.*;
import org.hibernate.criterion.*;

public class OrderOP {

SessionFactory sf;

     public OrderOP(){
                   Configuration cfg = new Configuration()
                           .addClass(Order.class);

                   sf = cfg.buildSessionFactory();

           }         

          public Order getOrder(String lower, String upper){
                        // open session
                       Session sess = sf.openSession();

                     //The following code has been commented so that
                   //comparison between HQL and Criteria Query

                /*String query = "select o from o "
               + "Order as o join o.products as p "
               + "where o.priceTotal > :priceTotalLower "
               + "and o.priceTotal < :priceTotalUpper";           

               Query q = sess.createQuery(query);
               q.setDouble("priceTotalLower", 
                                                Double.parseDouble(lower));

              q.setDouble("priceTotalUpper",
                                            Double.parseDouble(upper));
                    */
             List list = sess.createCriteria(Order.class)
                        .add(Restrictions.between(lower,upper)
                        . list();

            Order o=(Order)list.iterator.next();

           return o;
           }

          public static void main(String args[]){
                     Order o=OrderOP().getOrder(“2000’,”3000”);                 

                     System.out.println(“Order Id:”+ o.id);
                     //and so on
           }
}

You can see from the above code that if the object-oriented approach is really clear, then Criteria APIs are the easiest mode of data retrieval. That brings us to the end of this discussion. However, Hibernate is not just about CRUD operations. It is also about transaction and entity management as well as optimization techniques. These are topics that will be covered in the future.


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