With this example we are going to demonstrate how to retrieve objects in Hibernate with HQL query. In short, to retrieve objects in Hibernate with HQL query we have set the example below:
Employeeclass is the class whose objects will be inserted to the database.- In
RetrieveObjectsInHibernateWithHQLQuerywe use the Hibernate API to make the interface with the database. - We create a new
Configuration, that allows the application to specify properties and mapping documents to be used when creating aSessionFactory. Usually an application will create a singleConfiguration, build a single instance ofSessionFactoryand then instantiateSessionsin threads servicing client requests. Usingconfigure()API method we use the mappings and properties specified in an application resource namedhibernate.cfg.xml. Then, withbuildSessionFactory()we instantiate a newSessionFactory, using the properties and mappings in this configuration. - Use the
getCurrentSession()API method to obtain the current session. - Use the
beginTransaction()API method to begin a unit of work and return the associatedTransactionobject. If a new underlying transaction is required, begin the transaction. Otherwise continue the new work in the context of the existing underlying transaction. - Create a new
Query, using thecreateQuery(String queryString)API method of Session, with a given query. - Use the
list()API method of Query to get the results. - Use again
getTransaction()API method of Session andcommit()API method of Transaction to commit the Transaction.
In the code snippets that follow, you can see the Employee class, the RetrieveObjectsInHibernateWithHQLQuery Class that applies all above steps. You can also take a look at the hibernate.cfg.xml file, that holds all configuration for Hibernate, such as JDBC connection settings, and employee.hbm.xml file that holds the mapping configuration between the Employee class and the Employee table.
package com.javacodegeeks.snippets.enterprise;
import java.util.List;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class RetrieveObjectsInHibernateWithHQLQuery {
@SuppressWarnings("unchecked")
public static void main(String[] args) {
SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
Session session = sessionFactory.getCurrentSession();
try {
session.beginTransaction();
List<Employee> employees = (List<Employee>) session.createQuery("from Employee").list();
if (employees!=null) {
for (Employee employee : employees) {
System.out.println(employee.getId() + " - " + employee.getName());
}
}
session.getTransaction().commit();
}
catch (HibernateException e) {
e.printStackTrace();
session.getTransaction().rollback();
}
}
}
package com.javacodegeeks.snippets.enterprise;
import java.util.Date;
public class Employee {
private Long id;
private String name;
private String surname;
private String title;
private Date created;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSurname() {
return surname;
}
public void setSurname(String surname) {
this.surname = surname;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public Date getCreated() {
return created;
}
public void setCreated(Date created) {
this.created = created;
}
}
hibernate.cfg.xml
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<!-- JDBC connection settings -->
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="connection.url">jdbc:mysql://localhost/companydb</property>
<property name="connection.username">jcg</property>
<property name="connection.password">jcg</property>
<!-- JDBC connection pool, use Hibernate internal connection pool -->
<property name="connection.pool_size">5</property>
<!-- Defines the SQL dialect used in Hiberante's application -->
<property name="dialect">org.hibernate.dialect.MySQLDialect</property>
<!-- Enable Hibernate's automatic session context management -->
<property name="current_session_context_class">thread</property>
<!-- Disable the second-level cache -->
<property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>
<!-- Display and format all executed SQL to stdout -->
<property name="show_sql">true</property>
<property name="format_sql">true</property>
<!-- Drop and re-create the database schema on startup -->
<property name="hbm2ddl.auto">update</property>
<!-- Mapping to hibernate mapping files -->
<mapping resource="Employee.hbm.xml" />
</session-factory>
</hibernate-configuration>
Employee.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.javacodegeeks.snippets.enterprise.Employee" table="employee">
<id name="id" column="id">
<generator class="native"/>
</id>
<property name="name" not-null="true" length="50" />
<property name="surname" not-null="true" length="50" />
<property name="title" length="50" />
<property name="created" type="timestamp" />
</class>
</hibernate-mapping>
CREATE TABLE `companydb`.`employee` ( `id` INTEGER UNSIGNED NOT NULL AUTO_INCREMENT, `name` VARCHAR(45) NOT NULL, `surname` VARCHAR(45) NOT NULL, `title` VARCHAR(45) NOT NULL, `created` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP, PRIMARY KEY (`id`) );
Output:
Hibernate:
select
employee0_.id as id0_,
employee0_.name as name0_,
employee0_.surname as surname0_,
employee0_.title as title0_,
employee0_.created as created0_
from
employee employee0_
2 - Tom
3 - Jack
This was an example of how to retrieve objects in Hibernate with HQL query.
