HQL - Pagination
Say you are dealing with a web application and you are asked to show the data in pages. In that case Hibernate Pagination comes handy.
It can be achieved using the below methods:
- setFirstResult(int value) :
It defines the row number from which the value has to be fetched.
It starts from '0'.
- setMaxResults(int value) :
It fetches the number of rows mentioned in 'value'.
We will see in detail, how on combining the above two methods, pagination can be achieved.
Let us take the Employee class :
Employee
class Employee {
int id;
String name;
-- getters and setters --
}
There should be a simple mapping file for the same :
Employee.hbm.xml
<?xml version = "1.0" encoding = "utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name = "Employee" table = "EMPLOYEE">
<id name = "id" type = "string">
<column name = "ID">
</id>
<property name = "name" type = "string">
<column name = "NAME">
</property>
</class>
</hibernate-mapping>
Now, let us write the main() class and save three 'Employee' objects to database.
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class HibernateSave {
public static void main(String[] args) {
static SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
Session session = sessionFactory.openSession();
session.beginTransaction();
Employee employeeJoe = new Employee();
employee.setId(1);
employee.setName("Joe");
Employee employeePeter = new Employee();
employee.setId(2);
employee.setName("Peter");
session.save(employeePeter);
Employee employeeChang = new Employee();
employee.setId(3);
employee.setName("Chang");
session.save(employeeChang);
session.getTransaction().commit();
session.close();
sessionFactory.close();
}
}
EMPLOYEE
| ID |
NAME |
| 1 |
Joe |
| 2 |
Peter |
| 3 |
Chang |
How Pagination happens?
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class HibernateSave {
public static void main(String[] args) {
static SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
Session session = sessionFactory.openSession();
session.beginTransaction();
Query query = session.createQuery("from Employee");
query.setFirstResult(1);
query.setMaxResults(2);
session.getTransaction().commit();
session.close();
sessionFactory.close();
}
}
The below line tells Hibernate to fetch data from the second row(Since the count starts from '0').
query.setFirstResult(1);
And the next line tells Hibernate to fetch two rows from the second position.
query.setMaxResults(2);
And finally we get the below result.
