Hibernate supports a feature that helps us to build queries dynamically. The org.hibernate.Criteria is the interface used for this purpose. Criteria is useful when we are supposed to apply a multiple complicated search criteria on the queries.
For a Criteria query, a Criterion Object should be constructed (i.e) a call to createCriteria() passing the class of the objects we want the query to return.
Let us go the package com.demo.CriteriaExamples and execute the class CriteriaExampleExecutor.java
Criteria Example:
Following is an example that will all the instances of the class Employee.
Criteria criteria = session.createCriteria(Employee.class);
List critList = criteria.list();
for(Object objList: critList)
System.out.println("Employee Name is "+ ((Employee)objList).getEmpName());
Limiting the number of rows returned:
This is particularly useful in pagination.
Criteria criteria = session.createCriteria(Employee.class).setMaxResults(2);
critList = criteria.list();
System.out.println("Number of rows returned "+ critList.size());
for(Object objList: critList)
System.out.println("Employee Name is "+ ((Employee)objList).getEmpName());
Narrowing the result set:
Restrictions class provides factory methods for built-in Criterion types. In our example we have used some of the factory methods like Restrictions.like(), Restrictions.between(), Restrictions.isNotNull().
Criteria criteria = session.createCriteria(Employee.class).add(Restrictions.like("empName", "Ana%"));
critList = criteria.list();
for(Object objList: critList)
System.out.println("Employee Name is "+ ((Employee)objList).getEmpName());
Ordering the Result Set:
The class Order provides the factoy methods asc() and desc() to order objects based on any particular property.
Criteria criteria = session.createCriteria(Employee.class).addOrder(Order.asc("empName"))
.addOrder(Order.desc("salary"));
critList = criteria.list();
for(Object objList: critList)
System.out.println("Employee Name is "+ ((Employee)objList).getEmpName() + " Employee Salary is " + ((Employee)objList).getSalary());
Logical and Comparison Operators available in Restrictions Class:
All regular SQL comparison operators are available in the Restrictions class. The methods Restrictions.or() and Restrictions.and() will serve the Logical operators.
Criteria criteria = session.createCriteria(Employee.class).add(Restrictions.or(
Restrictions.gt("salary", new Integer(23000)), Restrictions.ge("age", new Integer(30))));
critList = criteria.list();
for(Object objList: critList)
System.out.println("Employee Name salary is more than 23000 or whose age is greater than or equal to 30 is "+ ((Employee)objList).getEmpName());
Aggregate Functions():
Projections class serves the factory methods which can be used as the aggregate functions as follows.
critList = session.createCriteria(Employee.class).setProjection(Projections.max("salary")).list();
System.out.println("Maximum salary is "+ critList.get(0));
critList = session.createCriteria(Employee.class).setProjection(Projections.min("salary")).list();
System.out.println("Minimum salary is "+ critList.get(0));
critList = session.createCriteria(Employee.class).setProjection(Projections.rowCount()).list();
System.out.println("Total employees "+ critList.get(0));
critList = session.createCriteria(Employee.class).setProjection(Projections.avg("age")).list();
System.out.println("Average employee age "+ critList.get(0));
critList = session.createCriteria(Employee.class).setProjection(Projections.sum("salary")).list();
System.out.println("Sum of all the salaries "+ critList.get(0));
Also, Projections class will help us to select exactly the objects or the properties of objects we need in the query result as follows.
session.createCriteria(Employee.class).setProjection(Projections.projectionList().add(Projections.id())
.add(Projections.property("empName"))
.add(Projections.property("age"))
);
