In this section we will discuss how to write subqueries using Detached Criteria in Hibernate.

Hibernate Detached Criteria Subquery

In this section we will discuss how to write subqueries using Detached Criteria  in Hibernate.

Hibernate Detached Criteria Subqueries :

By using Hibernate Criteria detached query you can write Hibernate subquries without caring the scope of session.
Detached criteria query is very good alternate when the hibernate session is not present.
By writing subqueries you can group, order and aggregate your resultant of query. Subqueries executed before the query run.

Here is syntax of writing hibernate detached criteria subquery -

DetachedCriteria query = DetachedCriteria.forClass(Employee.class)
.setProjection(Property.forName("salary").avg());
.......
.......
......
employeeList = session.createCriteria(Employee.class).add(
Subqueries.propertyGt("salary", query)).list();

Example : In this example we are showing how to write subquery using Criteria. Employee is our persistent class which maps employee table. In detachedCriteria query we are selecting the average salary. In subquery we are selecting records of employee whose salary is greater than average salary.

package net.roseindia.main;

import java.util.*;
import net.roseindia.table.Employee;
import net.roseindia.util.HibernateUtil;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.criterion.DetachedCriteria;
import org.hibernate.criterion.Property;
import org.hibernate.criterion.Subqueries;

public class DetachedCriteriaSubQuery {
public static void main(String[] args) {
DetachedCriteria query = DetachedCriteria.forClass(Employee.class)
.setProjection(Property.forName("salary").avg());

SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
Session session = sessionFactory.openSession();
List<Employee> employeeList = new ArrayList<Employee>();
employeeList = session.createCriteria(Employee.class).add(
Subqueries.propertyGt("salary", query)).list();
Iterator it = employeeList.iterator();
System.out.println(query.toString());
System.out.println("EmpId\tEmployee Name\tSalary\tDateOfJoin");
while (it.hasNext()) {
Employee employee = (Employee) it.next();
System.out.print(employee.getId());
System.out.print("\t" + employee.getName());
System.out.print("\t\t" + employee.getSalary());
System.out.print("\t" + employee.getDateOfJoin());
System.out.println();
}
session.close();

}
}

Output :

Hibernate: select this_.emp_id as emp1_0_0_, this_.date_of_join as date2_0_0_, this_.name as name0_0_, this_.salary as salary0_0_ from employee this_ where this_.salary > (select avg(this_.salary) as y0_ from employee this_)
EmpId     Employee Name     Salary     DateOfJoin
1         Mandy             20000      2010-03-12 00:00:00.0
2         Som               20000      1999-06-22 00:00:00.0
4         Roxi              22000      2001-02-03 00:00:00.0
5         Rowdy             20000      2012-06-27 00:00:00.0
6         Linda             20000      2010-06-12 00:00:00.0

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