Hibernate FROM Clause
In this tutorial you will learn how to use HQL from clause.
Use of FROM clause in hibernate is as same as it used in SQL for producing the tabular structure, this clause specifies the source table that is available to the other clause such as SELECT, DELETE.
Example :
Here I am giving a simple example which will demonstrate you how a HQL from clause can be used. To achieve the solution of such problem at first I have created a table named employee with the field 'Id' and 'Name'. Next created a POJO / Persistent class named Employee to fetch the persistent object, a hibernate.cfg.xml file that the Hibernate can utilize it to create connection pool and the required environment setup, an employee.hbm.xml file to map an Employee object with table employee. And finally create a simple java file into which we will use HQL from clause for selecting the data from the database.
Complete Code :
Employee.java
package roseindia;
public class Employee {
private int id;
private String name;
public Employee()
{
}
public Employee(String name)
{
this.name = name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
employee.hbm.xml
<?xml version='1.0'?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="roseindia"> <class name="Employee" table="employee"> <id name="id" type="int" column="Id" > <generator class="assigned"/> </id> <property name="name"> <column name="Name" /> </property> </class> </hibernate-mapping>
HibernateFromClause.java
package roseindia;
import java.util.List;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;
public class HibernateFromClause {
private static SessionFactory sessionFactory;
private static ServiceRegistry serviceRegistry;
public static void main(String args[]) {
Session session = null;
try {
try {
Configuration cfg = new Configuration().addResource(
"roseindia/employee.hbm.xml").configure();
serviceRegistry = new ServiceRegistryBuilder().applySettings(
cfg.getProperties()).buildServiceRegistry();
sessionFactory = cfg.buildSessionFactory(serviceRegistry);
} catch (Throwable th) {
System.err.println("Failed to create sessionFactory object."
+ th);
throw new ExceptionInInitializerError(th);
}
session = sessionFactory.openSession();
Query fromClause = session.createQuery("from Employee");
List<Employee> empList = fromClause.list();
for (Employee emp : empList) {
System.out.println("Id : " + emp.getId());
System.out.println("Name : " + emp.getName());
}
} catch (Exception e) {
System.out.println(e.getMessage());
} finally {
session.close();
}
}
}
hibernate.cfg.xml
<?xml version='1.0' encoding='utf-8'?> <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD//EN" "http://www.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.url">jdbc:mysql://192.168.10.13:3306/data </property> <property name="hibernate.connection.username">root</property> <property name="hibernate.connection.password">root</property> <property name="hibernate.connection.pool_size">10</property> <property name="show_sql">true</property> <property name="dialect">org.hibernate.dialect.MySQLDialect</property> <property name="hibernate.current_session_context_class">thread</property> </session-factory> </hibernate-configuration>
Output :
1. employee table
2. When you will execute the java file HibernateFromClause.java (RightClick -> runAs -> Java Application) you will get the output as :
