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Hibernate: Paving the Path for Queries


In the second part of our series on Hibernate, we will take a close look at its architecture and core classes. We will also cover the different types of queries possible in Hibernate. Finally, we'll use a real world example to illustrate our discussion.

Author Info:
By: A.P.Rajshekhar
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December 20, 2005
TABLE OF CONTENTS:
  1. · Hibernate: Paving the Path for Queries
  2. · Understanding the Architecture
  3. · Queries: Understanding the Types
  4. · In the Real World: Continued

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Hibernate: Paving the Path for Queries - In the Real World: Continued
(Page 4 of 4 )

Following is the code that was fetching the data according to the provided id:

package test;
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;
// use as
// java test. FindOrderById name
public class FindOrderById {
    public static void main(String[] args) throws Exception {
        // query to issue
        String query =
            "select order from Order "
             + "where order.id=:id";
        // search for what?
        String name = args[0];
        // init
        Configuration cfg = new Configuration()
                           .addClass(Order.class);
        SessionFactory sf = cfg.buildSessionFactory();
        // open session
        Session sess = sf.openSession();
       
        // search and return
        List list = sess.find(query, id,
                              Hibernate.STRING);
        if (list.size() == 0) {
            System.out.println("No Order having id "
                               + name);
            System.exit(0);
        }
        Order o = (Order) list.get(0);
        sess.close();
        System.out.println("Found Order: " + p);
    }
}

It is the bolded lines that will be changed. So let's get started.

The following is the above code rewritten using HQL. The bolded lines indicate the changes made.

package test;
import java.util.List;
//other imports
// use as
// java test. FindOrderById name
public class FindOrderById {
    public static void main(String[] args) throws Exception {
        // query to issue
        String query =
            "select order from Order "
             + "where order.id=:id";
        // search for what?
        String name = args[0];
        // init
        Configuration cfg = new Configuration()
                           .addClass(Order.class);
        SessionFactory sf = cfg.buildSessionFactory();
        // open session
        Session sess = sf.openSession();
       
        // search and return
      Query q = session.createQuery("from Order order where”+
                                                          +”order.id=:id");
      q.setString(“id”,name);
       List result = q.list();
        if (list.size() == 0) {
            System.out.println("No Order having id "
                               + name);
            System.exit(0);
        }
        Order o = (Order) list.get(0);
        sess.close();
        System.out.println("Found Order: " + p);
    }
}

Now let's do the same using QBC, which is as follows:

package test;
import java.util.List;
//other imports
// use as
// java test. FindOrderById name
public class FindOrderById {
    public static void main(String[] args) throws Exception {
        // query to issue
        String query =
            "select order from Order "
             + "where order.id=:id";
        // search for what?
        String name = args[0];
        // init
        Configuration cfg = new Configuration()
                           .addClass(Order.class);
        SessionFactory sf = cfg.buildSessionFactory();
        // open session
        Session sess = sf.openSession();
       
        // search and return
      Criteria criteria = session.createCriteria(Order.class);
      criteria.add( Expression.eq("id", name) );
      List result = criteria.list();
        if (list.size() == 0) {
            System.out.println("No Order having id "
                               + name);
            System.exit(0);
        }
        Order o = (Order) list.get(0);
        sess.close();
        System.out.println("Found Order: " + p);
    }
}

The main difference between HQL and QBC is clearly visible from the above codes. The HQL works just like SQL. But when QBC is used, the developer is working in a completely object oriented environment. Below is the code using QBE:

import java.util.List;
//other imports
// use as
// java test. FindOrderById name
public class FindOrderById {
    public static void main(String[] args) throws Exception {
        // query to issue
        String query =
            "select order from Order "
             + "where order.id=:id";
        // search for what?
        String name = args[0];
        // init
        Configuration cfg = new Configuration()
                           .addClass(Order.class);
        SessionFactory sf = cfg.buildSessionFactory();
        // open session
        Session sess = sf.openSession();
       
        // search and return
Order exampleOrder = new Order();
exampleOrder.setDate(new Date(1999,10,12);
Criteria criteria = session.createCriteria(Order.class);
criteria.add( Example.create(exampleOrder) );
List result = criteria.list();
        if (list.size() == 0) {
            System.out.println("No Order having Date "
                               + name);
            System.exit(0);
        }
        Order o = (Order) list.get(0);
        sess.close();
        System.out.println("Found Order: " + p);
    }
}

That ends this discussion of the architecture of Hibernate and the categories of the Queries. Now that the architecture is clear we can move on to more complex topics. In the next part I will discuss the life cycle of a persistent object and associations, as object life cycle becomes very important when working with associations. So, till next time.


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