Criteria Query, Hibernate Criteria Query Introduction

Unlike HQL, Criteria is only for selecting the data from the database, that to we can select complete objects only not partial objects, in fact by combining criteria and projections concept we can select partial objects too we will see this angle later,  😉 but for now see how we are using criteria for selecting complete objects form the database. We cant perform non-select operations using this criteria.  Criteria is suitable for executing dynamic queries too, let us see how to use this criteria queries in the hibernate..

syntax:

Criteria crit = session.createCriteria(–Our class object–);

Usage:

Criteria crit = session.createCriteria(Employee.class);
// let Product is our pojo class
List l = crit.list()
// need to call list() to execute criteria
Iterator it = l.iterator();
while(it.hasNext())
{
Object o = it.next();
Product p = (Product)o;
------ ----- -----
}

Adding Conditions To Criteria

• If we want to put conditions to load data from database, using criteria then we need to create one Criterion Interface object and we need to add this object to Criteria Class object

crit.add(Criterion Interface Object)
crit = criteria class object

• Criterion is an interface given in “org.hibernate.criterion” package
• In order to get Criterion object, we need to use Restrictions class
• Restrictions is the factory for producing Criterion objects, but friends there is no explicit relation between Criterion interface and Restrictions class, it means Restrictions class is not implemented from Criterion Interface
• In Restrictions class, we have all static methods and each method of this class returns Criterion object
• Restrictions class is also given in “org.hibernate.criterion” package

Usage:

Criteria crit = session.createCriteria(Products.class);
Criterion c1=Restrictions.gt("price", new Integer(12000));
//price is our pojo class variable
crit.add(c1); // adding criterion object to criteria class object
List l = crit.list(); // executing criteria query

Note: See line number 2, am calling gt(-,-) method of Restrictions class, (means greater than), in our above example am fetching the data by comparing price greater than (>) 12000

• If we want to put more conditions on the data (multiple conditions) then we can use and method , or method give by the Restrictions class

Usage:

crit.add(Restrictions.and(Restrictions.like("proName","%R%"),
Restrictions.eq("price",new Integer(12000))));
List l=crit.list();
Iterator it = l.iterator();

Like this we can add any number of conditions…

Let us see an example program on HQL criteria  in the next session…

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::. About the Author .::
		Sivateja Kandula - Java/J2EE Full Stack Developer Founder of Java4s - Get It Yourself, A popular Java/J2EE Programming Blog, Love Java and UI frameworks. You can sign-up for the Email Newsletter for your daily dose of Java tutorials.