Advertisement
Google Ad Slot: content-top
Hibernate Query Language
Hibernate Query Language (HQL) is an object-oriented query language similar to SQL, but designed for Hibernate. It operates on entity objects instead of database tables.
Select All Records:
- Equivalent to:
SELECT * FROM student; - Uses entity name (
Student) instead of table name.
import java.util.List;
Session session = HibernateUtil.getSession();
Transaction transaction = session.beginTransaction();
String hql = "FROM Student";
List students = session.createQuery(hql, Student.class).getResultList();
// Loop using for-each
for (Student student : students) {
System.out.println("Name: " + student.getName());
System.out.println("----------------------");
}
transaction.commit();
session.close();
Select Specific Columns:
- Returns specific fields instead of full entity objects.
import java.util.List;
String hql = "SELECT s.name, s.email FROM Student s";
List results = session.createQuery(hql,Object[].class).getResultList();
for (Object[] row : results) {
System.out.println("Name: " + row[0] + ", email: " + row[1]);
}
transaction.commit();
session.close();
HQL with WHERE Clause:
- Uses
:parameterto prevent SQL injection. - Equivalent SQL:
SELECT * FROM student WHERE name = 'Alice';
Session session = HibernateUtil.getSession();
Transaction transaction = session.beginTransaction();
String hql = "FROM Student WHERE name = :studentName";
Student student = session.createQuery(hql, Student.class)
.setParameter("studentName", "David")
.uniqueResult();
System.out.println(student.getEmail());
transaction.commit();
session.close();
Ordering Results:
ORDER BY
- Sorts results alphabetically by name.
String hql = "FROM Student ORDER BY name ASC";
List students = session.createQuery(hql, Student.class).getResultList();
ORDER BY DESC
- Sorts by age in descending order.
String hql = "FROM Student ORDER BY age DESC";
List students = session.createQuery(hql, Student.class).getResultList();
Filtering with LIKE (Pattern Matching):
- Fetches all students whose names start with 'A'.
String hql = "FROM Student WHERE name LIKE 'A%'";
List students = session.createQuery(hql, Student.class).getResultList();
HQL Joins:
Inner Join
- Fetches students enrolled in Java course.
String hql = "SELECT s FROM Student s INNER JOIN s.courses c WHERE c.title = 'Java'";
List students = session.createQuery(hql, Student.class).getResultList();
Left Join
- Includes students even if they don’t have courses.
String hql = "SELECT s FROM Student s LEFT JOIN s.courses c";
List students = session.createQuery(hql, Student.class).getResultList();
Fetch Join (Eager Loading)
- Prevents LazyInitializationException by eagerly fetching related entities.
String hql = "FROM Student s JOIN FETCH s.courses";
List students = session.createQuery(hql, Student.class).getResultList();
Aggregation Functions (COUNT, SUM, AVG, MIN, MAX):
Count Total Students
String hql = "SELECT COUNT(s) FROM Student s";
Long count = session.createQuery(hql, Long.class).getSingleResult();
Find Sum Age
String hql = "SELECT SUM(s) FROM Student s";
Integer count = session.createQuery(hql, Integer.class).getSingleResult();
Find Average Age
String hql = "SELECT AVG(s.age) FROM Student s";
Double avgAge = session.createQuery(hql, Double.class).getSingleResult();
Find Minimum Age
String hql = "SELECT MIN(s.age) FROM Student s";
Integer minAge = session.createQuery(hql, Integer.class).getSingleResult();
Find Maximum Age
String hql = "SELECT MAX(s.age) FROM Student s";
Integer minAge = session.createQuery(hql, Integer.class).getSingleResult();
Updating Data in HQL:
- Equivalent SQL:
UPDATE student SET age = 25 WHERE name = 'Alice';
String hql = "UPDATE Student SET age = :newAge WHERE name = :studentName";
int updatedCount = session.createQuery(hql)
.setParameter("newAge", 25)
.setParameter("studentName", "Alice")
.executeUpdate();
Deleting Data in HQL:
- Equivalent SQL:
DELETE FROM student WHERE name = 'Bob';
String hql = "DELETE FROM Student WHERE name = :studentName";
int deletedCount = session.createQuery(hql)
.setParameter("studentName", "Bob")
.executeUpdate();
Pagination in HQL:
Hibernate allows pagination using setFirstResult() and setMaxResults().
String hql = "FROM Student";
List students = session.createQuery(hql, Student.class)
.setFirstResult(5) // Skips first 5 records (Page 2)
.setMaxResults(5) // Fetch next 5 records
.getResultList();
Named Queries (@NamedQuery):
- A Named Query allows you to define HQL queries inside entity classes.
- Benefits: Code is cleaner & easier to maintain.
Defining Named Query:
@Entity
@NamedQuery(name = "Student.findByName", query = "FROM Student WHERE name = :name")
public class Student {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
}
Using Named Query:
List students = session.createNamedQuery("Student.findByName", Student.class)
.setParameter("name", "Alice")
.getResultList();