Benvenuti al tutorial sull’esempio di Hibernate Named Query. Abbiamo visto come possiamo utilizzare HQL e Query SQL nativa in Hibernate. Se ci sono molte query, esse causeranno confusione nel codice perché saranno sparse in tutto il progetto. Ecco perché Hibernate fornisce Named Query che possiamo definire in una posizione centrale e utilizzare ovunque nel codice. Possiamo creare named query sia per HQL che per SQL nativa.
Hibernate Named Query
La query nominata di Hibernate può essere definita nei file di mapping di Hibernate o attraverso l’uso delle annotazioni JPA @NamedQuery e @NamedNativeQuery. Oggi esamineremo entrambi e come utilizzare la query nominata di Hibernate in un’applicazione semplice. Utilizzeremo le stesse tabelle del database come nell’ Esempio HQL, quindi puoi controllare quel post per lo script SQL di configurazione del database. Per il nostro esempio di progetto di query nominata di Hibernate, utilizzeremo le annotazioni per il mapping di Hibernate. Tuttavia, creeremo alcune query nominate sia nei file di mapping che nelle classi dei bean di entità. La struttura finale del nostro progetto appare come nell’immagine sotto, ci concentreremo principalmente sui componenti relativi alla query nominata di Hibernate. 
Configurazione XML di Hibernate
hibernate.cfg.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration SYSTEM "https://hibernate.sourceforge.net/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" />
<mapping resource="named-queries.hbm.xml" />
</session-factory>
</hibernate-configuration>
Query XML denominata Hibernate
Abbiamo un file di mapping di Hibernate, che contiene solo query denominate HQL e query denominate SQL native. named-queries.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"https://hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<query name="HQL_GET_ALL_EMPLOYEE">from Employee</query>
<query name="HQL_GET_EMPLOYEE_BY_ID">
<![CDATA[from Employee where emp_id = :id]]>
</query>
<query name="HQL_GET_EMPLOYEE_BY_SALARY">
<![CDATA[from Employee where emp_salary > :salary]]>
</query>
<sql-query name="SQL_GET_ALL_EMPLOYEE">
<![CDATA[select emp_id, emp_name, emp_salary from Employee]]>
</sql-query>
<sql-query name="SQL_GET_ALL_EMP_ADDRESS">
<![CDATA[select {e.*}, {a.*} from Employee e join Address a ON e.emp_id=a.emp_id]]>
<return alias="e" class="com.journaldev.hibernate.model.Employee" />
<return-join alias="a" property="e.address"></return-join>
</sql-query>
</hibernate-mapping>
L’elemento query viene utilizzato per le query denominate HQL e l’elemento sql-query viene utilizzato per le query denominate SQL native. Possiamo utilizzare l’elemento return per dichiarare l’entità a cui verrà mappato il resultset. return-join viene utilizzato quando abbiamo una join di più tabelle. Dovremmo usare CDATA per dichiarare la nostra query denominata Hibernate per assicurarci che venga trattata come dati, altrimenti i segni < e > rovineranno il nostro file di mapping XML.
Query denominata HibernateAnnotazione @NamedQuery di Hibernate
Abbiamo due classi modello – Employee e Address. Abbiamo definito query denominate nella classe Address come segue.
package com.journaldev.hibernate.model;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.NamedNativeQueries;
import javax.persistence.NamedNativeQuery;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
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")
@NamedQueries({ @NamedQuery(name = "@HQL_GET_ALL_ADDRESS",
query = "from Address") })
@NamedNativeQueries({ @NamedNativeQuery(name = "@SQL_GET_ALL_ADDRESS",
query = "select emp_id, address_line1, city, zipcode from 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;
}
@Override
public String toString() {
return "AddressLine1= " + addressLine1 + ", City=" + city
+ ", Zipcode=" + zipcode;
}
}
Programma di test Hibernate Named Query
Scriviamo un programma di test per utilizzare tutte le query nominate di Hibernate definite sopra.
package com.journaldev.hibernate.main;
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.Address;
import com.journaldev.hibernate.model.Employee;
import com.journaldev.hibernate.util.HibernateUtil;
public class HibernateNamedQueryExample {
@SuppressWarnings("unchecked")
public static void main(String[] args) {
// Lavoro preliminare
SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
Session session = sessionFactory.getCurrentSession();
Transaction tx = session.beginTransaction();
// Esempio di query HQL nominata
Query query = session.getNamedQuery("HQL_GET_ALL_EMPLOYEE");
List empList = query.list();
for (Employee emp : empList) {
System.out.println("List of Employees::" + emp.getId() + ","
+ emp.getAddress().getCity());
}
query = session.getNamedQuery("HQL_GET_EMPLOYEE_BY_ID");
query.setInteger("id", 2);
Employee emp = (Employee) query.uniqueResult();
System.out.println("Employee Name=" + emp.getName() + ", City="
+ emp.getAddress().getCity());
query = session.getNamedQuery("HQL_GET_EMPLOYEE_BY_SALARY");
query.setInteger("salary", 200);
empList = query.list();
for (Employee emp1 : empList) {
System.out.println("List of Employees::" + emp1.getId() + ","
+ emp1.getSalary());
}
query = session.getNamedQuery("@HQL_GET_ALL_ADDRESS");
List addressList = query.list();
for (Address addr : addressList) {
System.out.println("List of Address::" + addr.getId() + "::"
+ addr.getZipcode() + "::" + addr.getEmployee().getName());
}
// Esempio di query SQL nativa nominata
query = session.getNamedQuery("@SQL_GET_ALL_ADDRESS");
List addressObjArray = query.list();
for(Object[] row : addressObjArray){
for(Object obj : row){
System.out.print(obj + "::");
}
System.out.println("\n");
}
query = session.getNamedQuery("SQL_GET_ALL_EMP_ADDRESS");
addressObjArray = query.list();
for(Object[] row : addressObjArray){
Employee e = (Employee) row[0];
System.out.println("Employee Info::"+e);
Address a = (Address) row[1];
System.out.println("Address Info::"+a);
}
// rollback per salvare i dati di test
tx.commit();
// chiusura delle risorse di Hibernate
sessionFactory.close();
}
}
Quando eseguiamo il programma sopra con i dati di test che abbiamo, produce il seguente output.
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 emp_id=?
Employee Name=David, City=Santa Clara
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 emp_salary>?
List of Employees::3,300.0
List of Employees::4,400.0
Hibernate: select address0_.emp_id as emp_id1_0_, address0_.address_line1 as address_2_0_, address0_.city as city3_0_, address0_.zipcode as zipcode4_0_ from ADDRESS address0_
List of Address::1::95129::Pankaj
List of Address::2::95051::David
List of Address::3::560100::Lisa
List of Address::4::100100::Jack
Hibernate: select emp_id, address_line1, city, zipcode from Address
1::Albany Dr::San Jose::95129::
2::Arques Ave::Santa Clara::95051::
3::BTM 1st Stage::Bangalore::560100::
4::City Centre::New Delhi::100100::
Hibernate: select e.emp_id as emp_id1_1_0_, e.emp_name as emp_name2_1_0_, e.emp_salary as emp_sala3_1_0_, a.emp_id as emp_id1_0_1_, a.address_line1 as address_2_0_1_, a.city as city3_0_1_, a.zipcode as zipcode4_0_1_ from Employee e join Address a ON e.emp_id=a.emp_id
Employee Info::Id= 1, Name= Pankaj, Salary= 100.0, {Address= AddressLine1= Albany Dr, City=San Jose, Zipcode=95129}
Address Info::AddressLine1= Albany Dr, City=San Jose, Zipcode=95129
Employee Info::Id= 2, Name= David, Salary= 200.0, {Address= AddressLine1= Arques Ave, City=Santa Clara, Zipcode=95051}
Address Info::AddressLine1= Arques Ave, City=Santa Clara, Zipcode=95051
Employee Info::Id= 3, Name= Lisa, Salary= 300.0, {Address= AddressLine1= BTM 1st Stage, City=Bangalore, Zipcode=560100}
Address Info::AddressLine1= BTM 1st Stage, City=Bangalore, Zipcode=560100
Employee Info::Id= 4, Name= Jack, Salary= 400.0, {Address= AddressLine1= City Centre, City=New Delhi, Zipcode=100100}
Address Info::AddressLine1= City Centre, City=New Delhi, Zipcode=100100
Punti importanti delle query nominate di Hibernate
Alcuni punti importanti sulle query nominate di Hibernate sono;
- La query nominata di Hibernate ci aiuta a raggruppare le query in una posizione centrale anziché lasciarle sparse in tutto il codice.
- La sintassi della query nominata di Hibernate viene verificata quando viene creata la session factory di Hibernate, rendendo così l’applicazione più veloce nel caso di errori nelle query nominate.
- La query nominata di Hibernate è globale, significa che una volta definita può essere utilizzata in tutta l’applicazione.
- Uno dei principali svantaggi della query nominata è che è difficile da debuggare, perché dobbiamo individuare la posizione in cui è definita.
E questo è tutto per l’esempio di query nominata di Hibernate, è possibile scaricare il progetto di esempio dal link sottostante.
Source:
https://www.digitalocean.com/community/tutorials/hibernate-named-query-example-namedquery