Hibernate SELECT Clause
In this tutorial you will learn how to use HQL select clause.
Use of SELECT clause in hibernate is as same as it used in SQL for selecting the data from the database.
Example :
Here I am giving a simple example which will demonstrate you how a HQL select 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 select 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>
HibernateSelectClause.java
package roseindia;
import java.util.List;
import java.util.Iterator;
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 HibernateSelectClause {
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();
//SELECT clause with from
Query selectClause = session.createQuery("select emp.id from Employee emp");
System.out.println("Displaying id from table employee");
for(Iterator<Integer> it= selectClause.iterate(); it.hasNext();){
Integer intr = it.next();
System.out.println("Employee Id : "+intr);
}
//SELECT clause with from & where
Query selectClause1 = session.createQuery("select emp.name from Employee emp where emp.id = 2");
List<String> empList1 = selectClause1.list();
System.out.println("Displaying Name from table employee whose id is 2");
for(String str : empList1)
{
System.out.println("Name : "+str);
}
} 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 HibernateSelectClause.java (RightClick -> runAs -> Java Application) you will get the output as :
