HQL - Hibernate Query Language - Example Tutorial

HQL or Hibernate Query Language is the object-oriented query language of Hibernate Framework. HQL is very similar to SQL except that we use Objects instead of table names, that makes it more close to object oriented programming.

Hibernate Query Language - HQL

HQL and Case Sensitivity: HQL is case-insensitive except for java class and variable names. So SeLeCT is the same as sELEct is the same as SELECT, but com.journaldev.model.Employee is not same as com.journaldev.model.EMPLOYEE. Some of the commonly supported clauses in HQL are:

1. HQL From: HQL From is same as select clause in SQL, from Employee is same as select * from Employee. We can also create alias such as from Employee emp or from Employee as emp.
2. HQL Join : HQL supports inner join, left outer join, right outer join and full join. For example, select e.name, a.city from Employee e INNER JOIN e.address a. In this query, Employee class should have a variable named address. We will look into it in the example code.
3. Aggregate Functions: HQL supports commonly used aggregate functions such as count(*), count(distinct x), min(), max(), avg() and sum().
4. Expressions: HQL supports arithmetic expressions (+, -, *, /), binary comparison operators (=, >=, <=, <>, !=, like), logical operations (and, or, not) etc.
5. HQL also supports ordre by and group by clauses.
6. HQL also supports sub-queries just like SQL queries.
7. HQL supports DDL, DML and executing store procedures too.

Let’s look at a simple example of using HQL in our program.

HQL Example Database Setup

I am using MySQL database for my example, below script will create two tables Employee and Address. They have one-to-one mapping and I am inserting some demo data for my example.

CREATE TABLE `Employee` (
  `emp_id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `emp_name` varchar(20) NOT NULL,
  `emp_salary` double(10,0) NOT NULL DEFAULT '0',
  PRIMARY KEY (`emp_id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;
 
CREATE TABLE `Address` (
  `emp_id` int(11) unsigned NOT NULL,
  `address_line1` varchar(50) NOT NULL DEFAULT '',
  `zipcode` varchar(10) DEFAULT NULL,
  `city` varchar(20) DEFAULT NULL,
  PRIMARY KEY (`emp_id`),
  CONSTRAINT `emp_fk_1` FOREIGN KEY (`emp_id`) REFERENCES `Employee` (`emp_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

INSERT INTO `Employee` (`emp_id`, `emp_name`, `emp_salary`)
VALUES
	(1, 'Pankaj', 100),
	(2, 'David', 200),
	(3, 'Lisa', 300),
	(4, 'Jack', 400);


INSERT INTO `Address` (`emp_id`, `address_line1`, `zipcode`, `city`)
VALUES
	(1, 'Albany Dr', '95129', 'San Jose'),
	(2, 'Arques Ave', '95051', 'Santa Clara'),
	(3, 'BTM 1st Stage', '560100', 'Bangalore'),
	(4, 'City Centre', '100100', 'New Delhi');
	
commit;

Create a maven project in Eclipse or the IDE you are using, our final project will look like below image.

Hibernate Maven Dependencies

Our final pom.xml contains dependencies for Hibernate and MySQL driver.

<project xmlns="https://maven.apache.org/POM/4.0.0" xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="https://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.journaldev.hibernate</groupId>
  <artifactId>HQLExample</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <dependencies>
  	<dependency>
  		<groupId>org.hibernate</groupId>
  		<artifactId>hibernate-core</artifactId>
  		<version>4.3.5.Final</version>
  	</dependency>
  	<dependency>
  		<groupId>mysql</groupId>
  		<artifactId>mysql-connector-java</artifactId>
  		<version>5.0.5</version>
  	</dependency>
  </dependencies>
</project>

Hibernate Configuration XML

Our hibernate configuration xml file contains database connection related properties and mapping classes. I will be using annotations for Hibernate mapping. hibernate.cfg.xml code:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
		"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
		"https://hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="hibernate.connection.password">pankaj123</property>
        <property name="hibernate.connection.url">jdbc:mysql://localhost/TestDB</property>
        <property name="hibernate.connection.username">pankaj</property>
        <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
        
        <property name="hibernate.current_session_context_class">thread</property>
        <property name="hibernate.show_sql">true</property>
        
        <mapping class="com.journaldev.hibernate.model.Employee"/>
        <mapping class="com.journaldev.hibernate.model.Address"/>
    </session-factory>
</hibernate-configuration>

Hibernate SessionFactory Utility class

We have a utility class to configure hibernate SessionFactory.

package com.journaldev.hibernate.util;

import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;

public class HibernateUtil {

	private static SessionFactory sessionFactory;
	
	private static SessionFactory buildSessionFactory() {
        try {
            // Create the SessionFactory from hibernate.cfg.xml
        	Configuration configuration = new Configuration();
        	configuration.configure("hibernate.cfg.xml");
        	System.out.println("Hibernate Configuration loaded");
        	
        	ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build();
        	System.out.println("Hibernate serviceRegistry created");
        	
        	SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);
        	
            return sessionFactory;
        }
        catch (Throwable ex) {
            System.err.println("Initial SessionFactory creation failed." + ex);
            ex.printStackTrace();
            throw new ExceptionInInitializerError(ex);
        }
    }
	
	public static SessionFactory getSessionFactory() {
		if(sessionFactory == null) sessionFactory = buildSessionFactory();
        return sessionFactory;
    }
}

Model Classes with Annotation based mapping

Our model classes with JPA annotations looks like below.

package com.journaldev.hibernate.model;

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

import org.hibernate.annotations.Cascade;

@Entity
@Table(name = "EMPLOYEE")
public class Employee {

	@Id
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	@Column(name = "emp_id")
	private long id;

	@Column(name = "emp_name")
	private String name;

	@Column(name = "emp_salary")
	private double salary;

	@OneToOne(mappedBy = "employee")
	@Cascade(value = org.hibernate.annotations.CascadeType.ALL)
	private Address address;

	public long getId() {
		return id;
	}

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

	public Address getAddress() {
		return address;
	}

	public void setAddress(Address address) {
		this.address = address;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public double getSalary() {
		return salary;
	}

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

}

package com.journaldev.hibernate.model;

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

import org.hibernate.annotations.GenericGenerator;
import org.hibernate.annotations.Parameter;

@Entity
@Table(name = "ADDRESS")
public class Address {

	@Id
	@Column(name = "emp_id", unique = true, nullable = false)
	@GeneratedValue(generator = "gen")
	@GenericGenerator(name = "gen", strategy = "foreign", 
				parameters = { @Parameter(name = "property", value = "employee") })
	private long id;

	@Column(name = "address_line1")
	private String addressLine1;

	@Column(name = "zipcode")
	private String zipcode;

	@Column(name = "city")
	private String city;

	@OneToOne
	@PrimaryKeyJoinColumn
	private Employee employee;

	public long getId() {
		return id;
	}

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

	public String getAddressLine1() {
		return addressLine1;
	}

	public void setAddressLine1(String addressLine1) {
		this.addressLine1 = addressLine1;
	}

	public String getZipcode() {
		return zipcode;
	}

	public void setZipcode(String zipcode) {
		this.zipcode = zipcode;
	}

	public String getCity() {
		return city;
	}

	public void setCity(String city) {
		this.city = city;
	}

	public Employee getEmployee() {
		return employee;
	}

	public void setEmployee(Employee employee) {
		this.employee = employee;
	}

}

HQL Example Test Class

Let’s see how to use HQL in java programs.

package com.journaldev.hibernate.main;

import java.util.Arrays;
import java.util.List;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;

import com.journaldev.hibernate.model.Employee;
import com.journaldev.hibernate.util.HibernateUtil;

public class HQLExamples {

	@SuppressWarnings("unchecked")
	public static void main(String[] args) {
		
		//Prep work
		SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
		Session session = sessionFactory.getCurrentSession();
		
		//HQL example - Get All Employees
		Transaction tx = session.beginTransaction();
		Query query = session.createQuery("from Employee");
		List<Employee> empList = query.list();
		for(Employee emp : empList){
			System.out.println("List of Employees::"+emp.getId()+","+emp.getAddress().getCity());
		}
		
		//HQL example - Get Employee with id
		query = session.createQuery("from Employee where id= :id");
		query.setLong("id", 3);
		Employee emp = (Employee) query.uniqueResult();
		System.out.println("Employee Name="+emp.getName()+", City="+emp.getAddress().getCity());
		
		//HQL pagination example
		query = session.createQuery("from Employee");
		query.setFirstResult(0); //starts with 0
		query.setFetchSize(2);
		empList = query.list();
		for(Employee emp4 : empList){
			System.out.println("Paginated Employees::"+emp4.getId()+","+emp4.getAddress().getCity());
		}
		
		//HQL Update Employee
		query = session.createQuery("update Employee set name= :name where id= :id");
		query.setParameter("name", "Pankaj Kumar");
		query.setLong("id", 1);
		int result = query.executeUpdate();
		System.out.println("Employee Update Status="+result);

		//HQL Delete Employee, we need to take care of foreign key constraints too
		query = session.createQuery("delete from Address where id= :id");
		query.setLong("id", 4);
		result = query.executeUpdate();
		System.out.println("Address Delete Status="+result);
		
		query = session.createQuery("delete from Employee where id= :id");
		query.setLong("id", 4);
		result = query.executeUpdate();
		System.out.println("Employee Delete Status="+result);
		
		//HQL Aggregate function examples
		query = session.createQuery("select sum(salary) from Employee");
		double sumSalary = (Double) query.uniqueResult();
		System.out.println("Sum of all Salaries= "+sumSalary);
		
		//HQL join examples
		query = session.createQuery("select e.name, a.city from Employee e "
				+ "INNER JOIN e.address a");
		List<Object[]> list = query.list();
		for(Object[] arr : list){
			System.out.println(Arrays.toString(arr));
		}
		
		//HQL group by and like example
		query = session.createQuery("select e.name, sum(e.salary), count(e)"
				+ " from Employee e where e.name like '%i%' group by e.name");
		List<Object[]> groupList = query.list();
		for(Object[] arr : groupList){
			System.out.println(Arrays.toString(arr));
		}
		
		//HQL order by example
		query = session.createQuery("from Employee e order by e.id desc");
		empList = query.list();
		for(Employee emp3 : empList){
			System.out.println("ID Desc Order Employee::"+emp3.getId()+","+emp3.getAddress().getCity());
		}
		
		//rolling back to save the test data
		tx.rollback();
		
		//closing hibernate resources
		sessionFactory.close();
	}

}

Notice that I am using HQL for Select, Update and Delete operations. It also shows how to use HQL Join and HQL Aggregate functions. When I run above hql example program, we get following output.

May 22, 2014 1:55:37 PM org.hibernate.annotations.common.reflection.java.JavaReflectionManager <clinit>
INFO: HCANN000001: Hibernate Commons Annotations {4.0.4.Final}
May 22, 2014 1:55:37 PM org.hibernate.Version logVersion
INFO: HHH000412: Hibernate Core {4.3.5.Final}
May 22, 2014 1:55:37 PM org.hibernate.cfg.Environment <clinit>
INFO: HHH000206: hibernate.properties not found
May 22, 2014 1:55:37 PM org.hibernate.cfg.Environment buildBytecodeProvider
INFO: HHH000021: Bytecode provider name : javassist
May 22, 2014 1:55:37 PM org.hibernate.cfg.Configuration configure
INFO: HHH000043: Configuring from resource: hibernate.cfg.xml
May 22, 2014 1:55:37 PM org.hibernate.cfg.Configuration getConfigurationInputStream
INFO: HHH000040: Configuration resource: hibernate.cfg.xml
May 22, 2014 1:55:37 PM org.hibernate.cfg.Configuration doConfigure
INFO: HHH000041: Configured SessionFactory: null
Hibernate Configuration loaded
Hibernate serviceRegistry created
May 22, 2014 1:55:37 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
WARN: HHH000402: Using Hibernate built-in connection pool (not for production use!)
May 22, 2014 1:55:37 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH000401: using driver [com.mysql.jdbc.Driver] at URL [jdbc:mysql://localhost/TestDB]
May 22, 2014 1:55:37 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH000046: Connection properties: {user=pankaj, password=****}
May 22, 2014 1:55:37 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH000006: Autocommit mode: false
May 22, 2014 1:55:37 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
INFO: HHH000115: Hibernate connection pool size: 20 (min=1)
May 22, 2014 1:55:37 PM org.hibernate.dialect.Dialect <init>
INFO: HHH000400: Using dialect: org.hibernate.dialect.MySQLDialect
May 22, 2014 1:55:37 PM org.hibernate.engine.jdbc.internal.LobCreatorBuilder useContextualLobCreation
INFO: HHH000423: Disabling contextual LOB creation as JDBC driver reported JDBC version [3] less than 4
May 22, 2014 1:55:38 PM org.hibernate.engine.transaction.internal.TransactionFactoryInitiator initiateService
INFO: HHH000399: Using default transaction strategy (direct JDBC transactions)
May 22, 2014 1:55:38 PM org.hibernate.hql.internal.ast.ASTQueryTranslatorFactory <init>
INFO: HHH000397: Using ASTQueryTranslatorFactory
Hibernate: select employee0_.emp_id as emp_id1_1_, employee0_.emp_name as emp_name2_1_, employee0_.emp_salary as emp_sala3_1_ from EMPLOYEE employee0_
Hibernate: select address0_.emp_id as emp_id1_0_0_, address0_.address_line1 as address_2_0_0_, address0_.city as city3_0_0_, address0_.zipcode as zipcode4_0_0_, employee1_.emp_id as emp_id1_1_1_, employee1_.emp_name as emp_name2_1_1_, employee1_.emp_salary as emp_sala3_1_1_ from ADDRESS address0_ left outer join EMPLOYEE employee1_ on address0_.emp_id=employee1_.emp_id where address0_.emp_id=?
Hibernate: select address0_.emp_id as emp_id1_0_0_, address0_.address_line1 as address_2_0_0_, address0_.city as city3_0_0_, address0_.zipcode as zipcode4_0_0_, employee1_.emp_id as emp_id1_1_1_, employee1_.emp_name as emp_name2_1_1_, employee1_.emp_salary as emp_sala3_1_1_ from ADDRESS address0_ left outer join EMPLOYEE employee1_ on address0_.emp_id=employee1_.emp_id where address0_.emp_id=?
Hibernate: select address0_.emp_id as emp_id1_0_0_, address0_.address_line1 as address_2_0_0_, address0_.city as city3_0_0_, address0_.zipcode as zipcode4_0_0_, employee1_.emp_id as emp_id1_1_1_, employee1_.emp_name as emp_name2_1_1_, employee1_.emp_salary as emp_sala3_1_1_ from ADDRESS address0_ left outer join EMPLOYEE employee1_ on address0_.emp_id=employee1_.emp_id where address0_.emp_id=?
Hibernate: select address0_.emp_id as emp_id1_0_0_, address0_.address_line1 as address_2_0_0_, address0_.city as city3_0_0_, address0_.zipcode as zipcode4_0_0_, employee1_.emp_id as emp_id1_1_1_, employee1_.emp_name as emp_name2_1_1_, employee1_.emp_salary as emp_sala3_1_1_ from ADDRESS address0_ left outer join EMPLOYEE employee1_ on address0_.emp_id=employee1_.emp_id where address0_.emp_id=?
List of Employees::1,San Jose
List of Employees::2,Santa Clara
List of Employees::3,Bangalore
List of Employees::4,New Delhi
Hibernate: select employee0_.emp_id as emp_id1_1_, employee0_.emp_name as emp_name2_1_, employee0_.emp_salary as emp_sala3_1_ from EMPLOYEE employee0_ where employee0_.emp_id=?
Employee Name=Lisa, City=Bangalore
Hibernate: select employee0_.emp_id as emp_id1_1_, employee0_.emp_name as emp_name2_1_, employee0_.emp_salary as emp_sala3_1_ from EMPLOYEE employee0_
Paginated Employees::1,San Jose
Paginated Employees::2,Santa Clara
Paginated Employees::3,Bangalore
Paginated Employees::4,New Delhi
Hibernate: update EMPLOYEE set emp_name=? where emp_id=?
Employee Update Status=1
Hibernate: delete from ADDRESS where emp_id=?
Address Delete Status=1
Hibernate: delete from EMPLOYEE where emp_id=?
Employee Delete Status=1
Hibernate: select sum(employee0_.emp_salary) as col_0_0_ from EMPLOYEE employee0_
Sum of all Salaries= 600.0
Hibernate: select employee0_.emp_name as col_0_0_, address1_.city as col_1_0_ from EMPLOYEE employee0_ inner join ADDRESS address1_ on employee0_.emp_id=address1_.emp_id
[Pankaj Kumar, San Jose]
[David, Santa Clara]
[Lisa, Bangalore]
Hibernate: select employee0_.emp_name as col_0_0_, sum(employee0_.emp_salary) as col_1_0_, count(employee0_.emp_id) as col_2_0_ from EMPLOYEE employee0_ where employee0_.emp_name like '%i%' group by employee0_.emp_name
[David, 200.0, 1]
[Lisa, 300.0, 1]
Hibernate: select employee0_.emp_id as emp_id1_1_, employee0_.emp_name as emp_name2_1_, employee0_.emp_salary as emp_sala3_1_ from EMPLOYEE employee0_ order by employee0_.emp_id desc
ID Desc Order Employee::3,Bangalore
ID Desc Order Employee::2,Santa Clara
ID Desc Order Employee::1,San Jose
May 22, 2014 1:55:38 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl stop
INFO: HHH000030: Cleaning up connection pool [jdbc:mysql://localhost/TestDB]

Notice that once delete operation is performed, further operations are not showing that record data (sum of salary is 600). However I am rolling back the transaction, so the data in table will remain unchanged. Change the code to commit the transaction and it will be reflected in the database tables. I don’t like using HQL query a lot because as you can see that we need to take care of table mappings in our code. If we will use Session to delete the Employee object, it will delete the record from both the tables. You can download the sample hql example project from below link and try more examples.

Download Hibernate HQL Project