Hibernate Criteria Query Language (HCQL)

• In Hibernate we pull the data from data base in two ways.
• session.get()/ session.load()
• Hibernate query langugae
• Now we will discuss about the third way Hibernate criteria query language which solves the problems of above two approaches.

Hibernate Criteria Query Language / HCQL

• In order to fetch the records based on some criteria we use Hibernate Criteria Query Language.
• We can make select operation on tables by applying some conditions by using HCQL.
• Criteria API is the alternative to HQL in object oriented approach.  
• We can execute only SELECT statements using Criteria; we can’t execute UPDATE, DELETE statements using Criteria.

Advantages of  Hibernate Criteria Query Language (HCQL) 

• Criteria API allows us to define criteria query object by applying rules ,filtration and logical conditions
• So that we can add criteria to query.
• Criteria is also database independent, Because it internally generates HQL queries.
• Criteria is suitable for executing dynamic queries
• Criteria API also include Query by Example (QBE) functionality for supplying example objects.
• Criteria also includes projection and aggregation methods
   

Criteria Interface:

• Criteria Interface has some methods to specify criteria.
• Hibernate session interface has a method named createCriteria() to create criteria.

1. public interface Criteria  extends CriteriaSpecification

1. Criteria criteria = session.createCriteria(Student.class);
2. List<Student> studentList= criteria .list();

Methods of Criteria interface:

  

Order Class

1. public class Order extends Object implements Serializable

 

• By using Order class we can sort the records in ascending or descending order.
• Order class provides two different methods to make ascending and descending.

1. public static Order asc(String propertyName)
2. public static Order desc(String propertyName)

Hibernate Criteria query example using order class

1.  Criteria criteria = session.createCriteria(Product.class)
2.  
3. // To sort records in descening order
4. criteria.addOrder(Order.desc("price"));
5.  
6. // To sort records in ascending order
7. criteria.addOrder(Order.asc("price"));

Restrictions Class

1. public class Restrictions extends Object

• Restrictions class provides methods that can be used  add restrictions (conditions) to criteria object.
• We have many methods in Restrictions class some of the commonly using methods are.

Hibernate Criteria query example using Restrictions class

1.  Criteria criteria = session.criteriaeateCriteria(Product.class);
2. // To get records having price more than 3000
3. criteria.add(Restrictions.gt("price", 3000));
4.  
5. // To get records having price less than 2000
6. criteria.add(Restrictions.lt("price", 2000));
7.  
8. // To get records having productName starting with criteriaite
9. criteria.add(Restrictions.like("productName", "criteriaite%"));
10.  
11. // Case sensitive form of the above restriction.
12. criteria.add(Restrictions.ilike("productName", "zara%"));
13.  
14. // To get records having price in between 1000 and 2000
15. criteria.add(Restrictions.between("price", 1000, 2000));
16.  
17. // To check if the given property price is null
18. criteria.add(Restrictions.isNull("price"));
19.  
20. // To check if the given property is not null
21. criteria.add(Restrictions.isNotNull("price"));
22.  
23. // To check if the given property price is empty
24. criteria.add(Restrictions.isEmpty("price"));
25.  
26. // To check if the given property price is not empty
27. criteria.add(Restrictions.isNotEmpty("price"));
28.  
29. List results = criteria.list();

Pagination using Hibernate Criteria

• By using criteria methods setFirstResult() and setMaxResults() we can achieve pagination concept.

1. Criteria criteria = session.createCriteria(Product.class);
2. criteria.setMaxResults(10);
3. criteria.setFirstResult(20);

Projections class in Hibernate

1. public final class Projections extends Object

• By Using org.hibernate.criterion.Projections  class methods we can perform operations like minimum , maximum, average , sum and count.

Hibernate Criteria query example using Projection class

1. Criteria criteria = session.criteriaeateCriteria(Product.class);
2.  
3. // To get total row count.
4. criteria.setProjection(Projections.rowCount());
5.  
6. // To get average price.
7. criteria.setProjection(Projections.avg("price"));
8.  
9. // To get distinct countof name
10. criteria.setProjection(Projections.countDistinct("name"));
11.  
12. // To get maximum price
13. criteria.setProjection(Projections.max("price"));
14.  
15. // To get minimum price
16. criteria.setProjection(Projections.min("price"));
17.  
18. // To get sum of price
19. criteria.setProjection(Projections.sum("price"))