HQL o Hibernate Query Language è il linguaggio di interrogazione orientato agli oggetti del framework Hibernate. HQL è molto simile a SQL tranne che per l’uso degli oggetti al posto dei nomi delle tabelle, il che lo rende più vicino alla programmazione orientata agli oggetti.
Linguaggio di interrogazione di Hibernate – HQL
HQL e Case Sensitivity: HQL non fa distinzione tra maiuscole e minuscole tranne che per i nomi delle classi e delle variabili java. Quindi SeLeCT è lo stesso di sELEct è lo stesso di SELECT, ma com.journaldev.model.Employee non è lo stesso di com.journaldev.model.EMPLOYEE. Alcune delle clausole comunemente supportate in HQL sono:
- HQL From: HQL From è lo stesso della clausola select in SQL,
from Employeeè lo stesso diselect * from Employee. Possiamo anche creare alias comefrom Employee empofrom Employee as emp. - HQL Join : HQL supporta inner join, left outer join, right outer join e full join. Ad esempio,
select e.name, a.city from Employee e INNER JOIN e.address a. In questa query, la classe Employee dovrebbe avere una variabile chiamata address. Lo esamineremo nel codice di esempio. - Funzioni di Aggregazione: HQL supporta le funzioni di aggregazione comunemente usate come count(*), count(distinct x), min(), max(), avg() e sum().
- Espressioni: HQL supporta espressioni aritmetiche (+, -, *, /), operatori di confronto binario (=, >=, <=, <>, !=, like), operazioni logiche (and, or, not) ecc.
- HQL supporta anche le clausole ordre by e group by.
- HQL supporta anche le sotto-query proprio come le query SQL.
- HQL supporta anche DDL, DML ed esecuzione di stored procedure.
Diamo uno sguardo a un esempio semplice di utilizzo di HQL nel nostro programma.
Setup del Database Esempio 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 progetto Maven in Eclipse o nell’IDE che stai usando, il nostro progetto finale avrà un aspetto simile all’immagine seguente. 
Dependency Maven di Hibernate
Il nostro pom.xml finale contiene le dipendenze per Hibernate e il driver 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>
Configurazione XML di Hibernate
Il nostro file di configurazione xml di Hibernate contiene proprietà relative alla connessione al database e classi di mapping. Utilizzerò le annotazioni per il mapping di Hibernate. Codice 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>
Classe di utilità SessionFactory di Hibernate
Abbiamo una classe di utilità per configurare la SessionFactory di 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 {
// Crea la SessionFactory da 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;
}
}
Classi modello con mapping basato su annotazioni
Le nostre classi modello con annotazioni JPA sono simili a quanto segue.
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;
}
}
Classe di esempio di test di HQL
Vediamo come utilizzare HQL nei programmi 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) {
//Lavoro preliminare
SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
Session session = sessionFactory.getCurrentSession();
//Esempio HQL - Ottieni tutti i dipendenti
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());
}
//Esempio HQL - Ottieni dipendente 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());
//Esempio di paginazione 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());
}
//Aggiorna dipendente 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);
//Elimina dipendente HQL, dobbiamo anche considerare vincoli di chiave esterna
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);
//Esempi di funzioni di aggregazione HQL
query = session.createQuery("select sum(salary) from Employee");
double sumSalary = (Double) query.uniqueResult();
System.out.println("Sum of all Salaries= "+sumSalary);
//Esempi di join 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));
}
//Esempio di raggruppamento e like 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));
}
//Esempio di ordinamento 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());
}
//Tornando indietro per salvare i dati di prova
tx.rollback();
//Chiusura delle risorse di Hibernate
sessionFactory.close();
}
}
Nota che sto usando HQL per le operazioni di Select, Update e Delete. Mostra anche come utilizzare HQL Join e le funzioni di aggregazione HQL. Quando eseguo il programma di esempio hql sopra, otteniamo il seguente 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]
Nota che una volta eseguita l’operazione di eliminazione, le operazioni successive non mostrano più i dati del record (la somma dello stipendio è 600). Tuttavia, sto annullando il rollback della transazione, quindi i dati nella tabella rimarranno invariati. Cambia il codice per confermare la transazione e ciò si rifletterà nelle tabelle del database. Non mi piace usare molto le query HQL perché, come puoi vedere, dobbiamo prendere cura dei mapping delle tabelle nel nostro codice. Se utilizzeremo la Session per eliminare l’oggetto Dipendente, verrà eliminato il record da entrambe le tabelle. Puoi scaricare il progetto di esempio hql dal link sottostante e provare più esempi.
Source:
https://www.digitalocean.com/community/tutorials/hibernate-query-language-hql-example-tutorial