HQL o Hibernate Query Language es el lenguaje de consulta orientado a objetos del Framework Hibernate. HQL es muy similar a SQL, excepto que utilizamos objetos en lugar de nombres de tablas, lo que lo acerca más a la programación orientada a objetos.
Lenguaje de Consulta de Hibernate – HQL
HQL y Sensibilidad a Mayúsculas y Minúsculas: HQL no distingue entre mayúsculas y minúsculas, excepto para los nombres de clases y variables en Java. Entonces, SeLeCT es lo mismo que sELEct, lo mismo que SELECT, pero com.journaldev.model.Employee no es lo mismo que com.journaldev.model.EMPLOYEE. Algunas de las cláusulas comúnmente admitidas en HQL son:
- HQL From: HQL From es lo mismo que la cláusula select en SQL,
from Employeees lo mismo queselect * from Employee. También podemos crear alias comofrom Employee empofrom Employee as emp. - HQL Join: HQL admite uniones internas, uniones externas izquierdas, uniones externas derechas y uniones completas. Por ejemplo,
select e.name, a.city from Employee e INNER JOIN e.address a. En esta consulta, la clase Employee debe tener una variable llamada address. Lo veremos en el código de ejemplo. - Funciones de Agregación: HQL admite funciones de agregación comúnmente utilizadas como count(*), count(distinct x), min(), max(), avg() y sum().
- Expresiones: HQL admite expresiones aritméticas (+, -, *, /), operadores de comparación binaria (=, >=, <=, <>, !=, like), operaciones lógicas (and, or, not), etc.
- HQL también soporta las cláusulas de ordenamiento (order by) y agrupamiento (group by).
- HQL también admite subconsultas al igual que las consultas SQL.
- HQL soporta DDL, DML y la ejecución de procedimientos almacenados también.
Veamos un ejemplo simple de cómo usar HQL en nuestro programa.
Configuración de la Base de Datos del Ejemplo de HQL
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;
Crea un proyecto Maven en Eclipse o en el IDE que estés usando, nuestro proyecto final se verá como en la imagen a continuación. 
Dependencias de Maven de Hibernate
Nuestro archivo pom.xml final contiene dependencias para Hibernate y el controlador MySQL.
<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>
Configuración XML de Hibernate
Nuestro archivo xml de configuración de hibernate contiene propiedades relacionadas con la conexión a la base de datos y clases de mapeo. Voy a utilizar anotaciones para el mapeo de Hibernate. Código hibernate.cfg.xml:
<?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>
Clase de utilidad de SessionFactory de Hibernate
Tenemos una clase de utilidad para configurar SessionFactory de hibernate.
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 {
// Crear la SessionFactory desde 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;
}
}
Clases de modelo con mapeo basado en anotaciones
Nuestras clases de modelo con anotaciones JPA se ven así:
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;
}
}
Clase de ejemplo de prueba de HQL
Vamos a ver cómo usar HQL en programas Java.
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) {
//Trabajo preliminar
SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
Session session = sessionFactory.getCurrentSession();
//Ejemplo de HQL - Obtener todos los empleados
Transaction tx = session.beginTransaction();
Query query = session.createQuery("from Employee");
List empList = query.list();
for(Employee emp : empList){
System.out.println("List of Employees::"+emp.getId()+","+emp.getAddress().getCity());
}
//Ejemplo de HQL - Obtener empleado con 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());
//Ejemplo de paginación de HQL
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());
}
//Actualizar empleado de HQL
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);
//Eliminar empleado de HQL, también debemos cuidar las restricciones de clave externa
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);
//Ejemplos de funciones de agregado de HQL
query = session.createQuery("select sum(salary) from Employee");
double sumSalary = (Double) query.uniqueResult();
System.out.println("Sum of all Salaries= "+sumSalary);
//Ejemplos de uniones de HQL
query = session.createQuery("select e.name, a.city from Employee e "
+ "INNER JOIN e.address a");
List list = query.list();
for(Object[] arr : list){
System.out.println(Arrays.toString(arr));
}
//Ejemplo de agrupar por y como en HQL
query = session.createQuery("select e.name, sum(e.salary), count(e)"
+ " from Employee e where e.name like '%i%' group by e.name");
List groupList = query.list();
for(Object[] arr : groupList){
System.out.println(Arrays.toString(arr));
}
//Ejemplo de ordenar por de HQL
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());
}
//regresar para guardar los datos de prueba
tx.rollback();
//cerrar recursos de hibernación
sessionFactory.close();
}
}
Tenga en cuenta que estoy usando HQL para operaciones de selección, actualización y eliminación. También muestra cómo usar HQL Join y HQL Aggregate functions. Cuando ejecuto el programa de ejemplo de HQL anterior, obtenemos la siguiente salida.
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]
Tenga en cuenta que una vez que se realiza la operación de eliminación, las operaciones posteriores no muestran esos datos de registro (la suma del salario es de 600). Sin embargo, estoy revirtiendo la transacción, por lo que los datos en la tabla permanecerán sin cambios. Cambie el código para confirmar la transacción y se reflejará en las tablas de la base de datos. No me gusta usar muchas consultas HQL porque, como puede ver, necesitamos cuidar los mapeos de tablas en nuestro código. Si usamos Session para eliminar el objeto Empleado, eliminará el registro de ambas tablas. Puede descargar el proyecto de ejemplo de HQL desde el siguiente enlace y probar más ejemplos.
Source:
https://www.digitalocean.com/community/tutorials/hibernate-query-language-hql-example-tutorial