NULL and NOT NULL comparison in the Hibernate API

null and not null check

While checking for the null and not null values in the Hibernate API, we have to be careful and there is chance for misunderstanding. This tips explains how to compare the null values in the Hibernate query.

also read:

• Introduction to Hibernate
• Hibernate Interview Questions
• Interceptors in Hibernate
• Hibernate Books

In Java language, if object==null will return the proper value if it is null or not. That means null==null will returns true in the programming. But, the same scenario is differenet in the database world. if you check for null==null in the query, it will retrun false. That is why database provide a “IS NULL” keyword to check the null values. Hibernate provides equaivalent methods to check the null values. Look into the following example code for more details:

JavaBeatHibernateExample.java

[code lang=”java”]
package javabeat.net.hibernate;

import java.util.List;
import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.criterion.Expression;

/**
* source : www.javabeat.net
*/
public class JavaBeatHibernateExample {
public static void main(String args[]) {
Configuration configuration = new Configuration();
// configuring hibernate
SessionFactory sessionFactory = configuration.configure().buildSessionFactory();
Session session = sessionFactory.openSession();
Criteria criteria = session.createCriteria(Student.class);
criteria.add(Expression.isNotNull("name"));
List<Student> list = criteria.list();
for (Student student : list){
System.out.println(student.getName());
}
}
}

[/code]

In the above code,Expression.isNotNull(“name”) is used for checking the particular colimn for the null values. All the non null rows will be returned for the above code. In the same way you can check for the null values like this:Expression.isNull(“name”)