Hibernate Criteria Query
In this tutorial you will learn about the Hibernate Criteria Query.
Hibernate provides an API for writing the dynamic query in an elegant way to execute . Except the use of HQL in Hibernate, Criteria query is an another way to write query it provides a more object orientation feature. When using a Criteria Query an application developer will required to use the provided API this is because when an application developer uses the HQL they must have the knowledge of SQL queries but the Criteria Query APIs provided by Hibernate maps the SQL functionality to the objects.
In applications the following native APIs are required to use :
- Criteria : A simplified API that retrieve entities from the contained or composed Criterion objects. This approach is very useful for the "search" function when a different number of fields are composed by the restrictions query.
public interface Criteria extends CriteriaSpecification
for example
Criteria criteria = session.createCriteria(Employee.class);
criteria.add(Restrictions.like("empName", "%n%"));
criteria.setMaxResults(15);
List emp = criteria.list();
Criteria interface provides the various methods some of them are as follows :
| Methods | Description |
| add(Criterion criterion) | adds a Criterion to constrain the results to be retrieved. |
| addOrder (Order order) | Order to the result set is added. |
| createAlias () | Join an association, assigning an alias to the joined entity. |
| createCriteria () | Used for creating a new Criteria, "rooted" at the associated entity. |
| setMaxResults (int maxResult) | Used to set a maximum limit upon the number of objects to be fetched. |
| uniqueResult() | Used to instruct the Hibernate to retrieve and return the unique records from database. |
public interface Criterion extends Serializable
Criterion interface provides the following methods :
| Method | Description |
| getTypedValues() | Use to give back the typed values for all parameters. |
| toSqlString() | gives the SQL fragment. |
public class Restrictions extends Object
This class provides the static methods some of them are as follows :
| Method | Description |
| allEq() | Used to apply an "equals" constraint to each property in the key set of a Map |
| and() | Gives the conjunction of two expressions |
| or() | Gives the disjunction of two expressions |
| not() | Gives the negation of an expression |
| in() | Used to apply an "in" constraint to the specified property |
| ge() | Used to apply a "greater than or equal" constraint to the specified property |
| le() | Used to apply a "less than or equal" constraint to the specified property |
public final class Projections extends Object
This class provides the static methods some of them are as follows :
| Method | Description |
| alias() | Using this method a projection is to be assigned an alias by wrapping it |
| avg() | Returns an average value of a property. |
| count() | Returns a count of a property. |
| id() | It specifies the projected identifier value |
public class Order extends Object implements Serializable
This class provides methods to imposed the order upon result set some of them are as follows :
| Method | Description |
| asc(String propertyName) | This is used to arrange the result set in ascending order. |
| desc(String propertyName) | This is used to arrange the result set in descending order. |