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So far, you have seen how to execute commands in Hibernate Query Language (HQL) which are slightly different from SQL commands. For those who are somehow uncomfortable with learning Hibernate Query Language to interact with the database, don't worry, Hibernate has got a solution. Hibernate also provides a way to execute the SQL queries by using its method createNativeQuery() of Query class.


Today, we are going to show you how to execute the SQL commands like accessing multiple columns of a table and executing SQL methods like max(), min(), sum(), count() and avg() using Hibernate.

Note :

• In the upcoming example, We are going to create a Java class which will be mapped to a table in our database(Oracle Express Edition 10g). We are going to use some Hibernate Annotations, hence, there will be no need to create the mapping-resource with extension hbm.xml . For those who are not aware of Hibernate Annotations, please read Hibernate Annotations for reference.


• And yes, one more thing, we are going to create this program in an Integrated Development Environment (IDE), so you may use any IDE of your choice.







Creating an Entity class



We are going to create a general parent class that will contain all the Java code files representing our Model class(whose objects needs to be persisted).

This is a simple Java class whose objects needs to be persisted/saved, these objects are also known as Plain Old Java Objects(POJO) or Entity class. Some may even refer to such class whose objects needs to be persisted as the Model class. This class is an entity class, hence it will be preceded with the @Entity annotation plus a few other annotations used below.


UserInfo.java

package decodejava;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table (name ="USER_INFO")
public class UserInfo {
@Id
@GeneratedValue
@Column (name = "ID")
private int id;
	
@Column (name = "First_Name")
private String firstName;
	
@Column (name = "Salary")
private Integer salary;	
	
	
public int getId()
{
	return id;
}
	


public void setId(int id) 
{
	this.id = id;
}
	

public String getFirstName() 
{
	return firstName;
}


public void setFirstName(String firstName) 
{
	this.firstName = firstName;
}



public Integer getSalary() 
{
	return salary;
}



public void setSalary(Integer salary) 
{
	this.salary = salary;
}
}






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Creating the class that calls the Hibernate API


This class will create some UserInfo objects, which will be persisted in a database table using the Hibernate and then it's going to execute the SQL commands like accessing multiple columns of a table and executing SQL methods like max(), min(), sum(), count() and avg() using the method createNativeQuery() of Query class.

The Hiber class creates a Configuration object, used to configure the Hibernate. This is the first object we use when using the Hibernate. This object is used to specify the location of a configuration file and mapping document used by Hibernate. Using Configuration object we can create a SessionFactory object, which is eventually used to create a Session object to perform the object persistence operations.


Hiber.java

package decodejava;

import java.util.List;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;

//import javax.persistence.Parameter;
//import javax.persistence.Query;

public class Hiber 
{

	public static void main(String[] args) 
	{

	SessionFactory sf=  new Configuration().configure().buildSessionFactory();  
	Session session = sf.openSession();

	
	
	//Creating the first object
	UserInfo ob1 = new UserInfo();
	ob1.setFirstName("D");
	ob1.setSalary(40000);

	
	//Creating the second object
	UserInfo ob2 = new UserInfo();
	ob2.setFirstName("A");
	ob2.setSalary(20000);

	
	//Creating the third object
	UserInfo ob3 = new UserInfo();
	ob3.setFirstName("Z");
	ob3.setSalary(35000);

	

	session.beginTransaction();
	session.save(ob1); //Saving the first object
	session.save(ob2); //Saving the second object
	session.save(ob3); //Saving the third object
	session.getTransaction().commit();
	session.close();
	
	
	
	//Opening a new Session
	session = sf.openSession();
	
	
	//Beginning the Transaction
	session.beginTransaction();
				
	
	//Creating a Query by calling createNativeQuery() method to execute an SQL query 
	Query query = session.createNativeQuery("select ID,First_Name from User_Info");
	List<Object[]> collection = query1.getResultList();
				
	System.out.println("Retrieving values in multiple columns with property 'id' and 'firstName' ");
	 for(Object[] user: collection)
	 {
		 System.out.println("Id : " + user[0]);
		 System.out.println("First Name : " + user[1]);
		 System.out.println();
	 }
					
							
				
	//Creating a Query by calling createNativeQuery() method to execute SQL min() function
	query = session.createNativeQuery("select min(salary) from User_Info");
	Object o1 = query.getSingleResult();
	System.out.println("Minimum Salary :" +o1);
	System.out.println();
	
	
	
	//Creating a Query by calling createNativeQuery() method to execute SQL max() function
	query = session.createNativeQuery("select max(salary) from User_Info");
	o1 = query.getSingleResult();
	System.out.println("Maximum Salary :" + o1);
	System.out.println();
	
	
	
	//Creating a Query by calling createNativeQuery() method to execute SQL avg() function
	query = session.createNativeQuery("select avg(salary) from User_Info");
	o1 = query.getSingleResult();
	System.out.println("Average Salary :" + o1);
	System.out.println();
	
	
	
	//Creating a Query by calling createNativeQuery() method to execute SQL count() function
	query = session.createNativeQuery("select count(id) from User_Info");
	o1 = query.getSingleResult();
	System.out.println("Total count of IDs :" + o1);
	System.out.println();
	
	
	
	//Creating a Query by calling createNativeQuery() method to execute SQL sum() function
	query = session.createNativeQuery("select sum(salary) from User_Info");
	o1 = query.getSingleResult();
	System.out.println("Total sum of salaries :" + o1);
	
	System.out.println();
	
	

	//Committing the Transaction					
	session.getTransaction().commit();
						
						
	//closing the session
	session.close();
	}
}








Adding JARs



• We are going to add some JARs files to the build path of our Java project. These JARs make the Hibernate work with our database using a specific JDBC Driver for our particular database.
  
  All these JARs are included in the folder named required(within our Hibernate installation folder). So, we need to add all the JARs in the required to our build path of our Java project.
  
  
• Finally, we are going to add one more JAR file. This is a specific JDBC JAR file(ojdbc14.jar) required by Hibernate to connect to our database(Oracle Express Edition 10g) and perform object-relational mapping and object persistence.


Note : Those who don't know how to add JARs to the build path of your Java project in Eclipse IDE, please refer to our section Adding JARs to your Hibernate project in Eclipse.







Adding a configuration file



• Next, we are going to add a configuration file to our project.
  
  This configuration document ends with an extension .cfg.xml, and it is named as hibernate.cfg.xml.
  
  
  This configuration file is an xml file and it allows us to specify the following features -
  • A database to which Hibernate connects to perform object-relational mapping and object persistence.
  • The JDBC driver class for our specific database, used by the Hibernate to connect to the database.
  • The username and password of database, using which the Hibernate connects to the database.
  • An SQL Dialect, used by the Hibernate to instruct the database.
  • A Entity/POJO class which will be mapped to a database table by Hibernate.
  • A command to echo all the SQL commands which are executed by the Hibernate on stdout.
  • The mapping entity class, used by Hibernate to correctly map the class(UserInfo) to a database table.
  
  
  
  hibernate.cfg.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">



<hibernate-configuration>

<session-factory>


<!-- Database connection settings -->
<property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
<property name="connection.url">jdbc:oracle:thin:@localhost:1521:XE</property>
<property name="connection.username">system</property>
<property name="connection.password">promila21</property>


<!-- JDBC connection pool (use the built-in) -->
<property name="connection.pool_size">1</property>


<!-- SQL dialect -->
<property name="dialect">org.hibernate.dialect.Oracle10gDialect</property>


<!-- Disable the second-level cache  -->
<property name="cache.provider_class">org.hibernate.cache.internal.NoCacheProvider</property>
        
        
<!-- Echo all executed SQL to stdout -->
<property name="show_sql">true</property>


<!-- Drop and re-create the database schema on startup -->
<property name="hbm2ddl.auto">create</property>


<!-- Names the mapping entity class -->
<mapping class ="decodejava.UserInfo"/>


</session-factory>

</hibernate-configuration>








Directory Structure of Hibernate Project






The picture above depicts how and where to arrange POJO/Entity(.java) file and the class(that calls the hibernate into action) in a specific directory structure.

Project Folder - HQLExecutingSQLQueries is the name of our Project and it is a top-level directory.


• This project folder contains the main package of our project i.e. decodejava, which contains POJO/Entity class file i.e. UserInfo.java and the class that calls the hibernate into action i.e. Hiber.java.



• Besides this, the project folder also contains the hibernate configuration file i.e. hibernate.cfg.xml, and as we have used some Hibernate Annotations in this project, hence, there will be no need to create the mapping-resource with extension hbm.xml .



• The project folder also contains all the needed Hibernate JARs present in the required folder of Hibernate installation and the JDBC JAR file(ojdbc14.jar) required by Hibernate to connect to our database.







Execution


When you execute the Hiber.java class, you will see the following output -



Hibernate: create sequence hibernate_sequence start with 1 increment by 1
Hibernate: create table USER_INFO (ID number(10,0) not null, First_Name varchar2(255 char), Salary number(10,0), primary key (ID))
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: insert into USER_INFO (First_Name, Salary, ID) values (?, ?, ?)
Hibernate: insert into USER_INFO (First_Name, Salary, ID) values (?, ?, ?)
Hibernate: insert into USER_INFO (First_Name, Salary, ID) values (?, ?, ?)
Hibernate: select ID,First_Name from User_Info
Retrieving values in multiple columns with property 'id' and 'firstName' 
Id : 1
First Name : First

Id : 2
First Name : Second

Id : 3
First Name : Third

Hibernate: select min(salary) from User_Info
Minimum Salary :20000

Hibernate: select max(salary) from User_Info
Maximum Salary :40000

Hibernate: select avg(salary) from User_Info
Average Salary :31666.6666666666666666666666666666666667

Hibernate: select count(id) from User_Info
Total count of IDs :3

Hibernate: select sum(salary) from User_Info
Total sum of salaries :95000


This output shows you all the SQL commands executed by the Hibernate within the database to create the tables and save three objects, retrieving multiple columns, executing of SQL queries max(), min(), sum(), count(), avg() functions.


After executing Hiber class, a tables will be created in the database with the name User_Info.


Additionally, let's query the database and see what are the contents of this table.



• select * from User_Info 








This table shows you the objects of class UserInfo class mapped by Hibernate to a table named User_Info in the database.






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