Hibernate Subqueries

In this section, you will learn about the subqueries with an appropriate example.

Subqueries in hibernate can be referred as the queries that are surrounded by parentheses (). Subqueries solves the purpose of grouping, ordering , narrowing and aggregating the resultant of the query by using the where clause. Notice that the subqueries get executed prior to the main query. The HQL queries may contain the subqueries only in case of if the subqueries are supported by the underline database.

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 this example 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. And the we retrieve the data from the database store it in that Query object and iterate this object with the help of Iterator and finally displays the requested data on the console.


package net.roseindia;



import java.util.Iterator;

import java.util.List;



import org.hibernate.Query;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.cfg.Configuration;



public class Subqueries {



  /**

   * @param args

   */

  public static void main(String[] args) {

    // TODO Auto-generated method stub

    Session sess = null;

    try{

      SessionFactory fact = new Configuration().configure().buildSessionFactory();

      sess = fact.openSession();

      String sql_query = "select d.name,p.name,p.price from Product p join p.dealer 

d where p.price in(select p.price from p where p.price > 1500)";

      Query query = sess.createQuery(sql_query);

      System.out.println("Dealer Name\t"+"Product Name\t"+"Price");

      for(Iterator it=query.iterate();it.hasNext();){

        Object[] row = (Object[]) it.next();

        System.out.print(row[0]);

        System.out.print("\t\t"+row[1]);

        System.out.print("\t"+row[2]);

        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 dealer1_.name as col_0_0_, product0_.name as col_1_0_, product0_.price as col_2_0_ from Product product0_ inner join Dealer dealer1_ on product0_.did=dealer1_.id where product0_.price in (select product0_.price from Product product0_ where product0_.price>1500)

Dealer Name Product Name Price

Agrawal Computer 23000.0

Mohan Mobile 15000.0

Ritu HardDisk 2500.0