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Hibernate
Hibernate Criteria API

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The Criteria API is an alternative to HQL (Hibernate Query Language) for writing dynamic queries in Hibernate. Instead of writing queries as plain strings, Criteria API allows type-safe, object-oriented queries.


Why Use Criteria API?

✅ Dynamic Queries – Queries can be built at runtime.

✅ Type-Safe – Uses Java classes instead of raw strings.

✅ No String-Based HQL – Avoids syntax errors from misspelled query strings.

✅ Better Maintainability – Queries are constructed programmatically.

Setting Up Criteria API

To use Criteria API, you need to get a Session and use the CriteriaBuilder class.

HibernateUtil.java
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {
private static final SessionFactory sessionFactory = buildSessionFactory();

private static SessionFactory buildSessionFactory() {
try {
return new Configuration()
.configure("hibernate.cfg.xml")
.addAnnotatedClass(Person.class)
.addAnnotatedClass(Course.class)
.buildSessionFactory();
} catch (Throwable ex) {
System.err.println("SessionFactory creation failed: " + ex);
throw new ExceptionInInitializerError(ex);
}
}

public static SessionFactory getSessionFactory() {
return sessionFactory;
}

public static Session getSession() {
return sessionFactory.openSession(); // Opens a new session when needed
}

public static void shutdown() {
sessionFactory.close(); // Close SessionFactory when the application shuts down
}
}
Session session = HibernateUtil.getSession();
CriteriaBuilder builder = session.getCriteriaBuilder();

Fetch All Records (Equivalent to SELECT * FROM table):

Session session = HibernateUtil.getSession();
CriteriaBuilder builder = session.getCriteriaBuilder();
CriteriaQuery<Student> query = builder.createQuery(Student.class);
Root<Student> root = query.from(Student.class);
query.select(root);

List<Student> students = session.createQuery(query).getResultList();
System.out.println(students);
session.close();

Applying WHERE Condition

🔹 Fetch Students with Age > 20

🔹 Equivalent SQL: SELECT * FROM student WHERE age > 20;

CriteriaBuilder builder = session.getCriteriaBuilder();
CriteriaQuery<Student> query = builder.createQuery(Student.class);
Root<Student> root = query.from(Student.class);
query.select(root).where(builder.gt(root.get("age"), 20));

List<Student> students = session.createQuery(query).getResultList();

Applying Multiple Conditions (AND, OR)

🔹 Fetch Students where age > 20 AND name starts with 'A'

🔹 Equivalent SQL: SELECT * FROM student WHERE age > 20 AND name LIKE 'A%';

CriteriaBuilder builder = session.getCriteriaBuilder();
CriteriaQuery<Student> query = builder.createQuery(Student.class);
Root<Student> root = query.from(Student.class);

Predicate agePredicate = builder.gt(root.get("age"), 20);
Predicate namePredicate = builder.like(root.get("name"), "A%");

query.select(root).where(builder.and(agePredicate, namePredicate));

List<Student> students = session.createQuery(query).getResultList();

Sorting Results (ORDER BY)

🔹 Sort Students by Age (Ascending)

🔹 Equivalent SQL: SELECT * FROM student ORDER BY age ASC;


CriteriaBuilder builder = session.getCriteriaBuilder();
CriteriaQuery<Student> query = builder.createQuery(Student.class);
Root<Student> root = query.from(Student.class);

query.select(root).orderBy(builder.asc(root.get("age")));

List<Student> students = session.createQuery(query).getResultList();

🔹 Sort Students by Name (Descending)

🔹 Equivalent SQL: SELECT * FROM student ORDER BY name DESC;

query.orderBy(builder.desc(root.get("name")));

Fetching Specific Columns

🔹 Select Only Name and Age

🔹 Equivalent SQL: SELECT name, age FROM student;

CriteriaBuilder builder = session.getCriteriaBuilder();
CriteriaQuery<Object[]> query = builder.createQuery(Object[].class);
Root<Student> root = query.from(Student.class);

query.multiselect(root.get("name"), root.get("age"));

List<Object[]> results = session.createQuery(query).getResultList();
for (Object[] row : results) {
System.out.println("Name: " + row[0] + ", Age: " + row[1]);
}

Aggregation Functions (COUNT, SUM, AVG, MIN, MAX)

🔹 Count Total Students

🔹 Equivalent SQL: SELECT COUNT(*) FROM student;

CriteriaBuilder builder = session.getCriteriaBuilder();
CriteriaQuery<Long> query = builder.createQuery(Long.class);
Root<Student> root = query.from(Student.class);

query.select(builder.count(root));

Long count = session.createQuery(query).getSingleResult();
System.out.println("Total Students: " + count);

🔹 Find Average Age

🔹 Equivalent SQL: SELECT AVG(age) FROM student;

query.select(builder.avg(root.get("age")));

Using Joins in Criteria API

🔹 Inner Join (Fetch Students with their Courses)

🔹 Equivalent SQL: SELECT * FROM student JOIN course ON student.id = course.student_id;

CriteriaBuilder builder = session.getCriteriaBuilder();
CriteriaQuery<Student> query = builder.createQuery(Student.class);
Root<Student> root = query.from(Student.class);

Join<Student, Course> courseJoin = root.join("courses"); // Assuming 'courses' is a List<Course>
query.select(root);

List<Student> students = session.createQuery(query).getResultList();

🔹 Left Join (Fetch Students Even If They Have No Courses)

🔹 Equivalent SQL: SELECT * FROM student LEFT JOIN course ON student.id = course.student_id;

Join<Student, Course> courseJoin = root.join("courses", JoinType.LEFT);

Pagination (Limit & Offset)

Hibernate Criteria API allows pagination using setFirstResult() and setMaxResults().

🔹 Fetch Page 2 (5 Records Per Page)

🔹 Equivalent SQL: SELECT * FROM student LIMIT 5 OFFSET 5;

List<Student> students = session.createQuery(query)
.setFirstResult(5) // Skip first 5 records (Page 2)
.setMaxResults(5) // Fetch next 5 records
.getResultList();

Deleting Data using Criteria API

🔹 Equivalent SQL: DELETE FROM student WHERE name = 'John';

CriteriaBuilder builder = session.getCriteriaBuilder();
CriteriaDelete<Student> deleteQuery = builder.createCriteriaDelete(Student.class);
Root<Student> root = deleteQuery.from(Student.class);

deleteQuery.where(builder.equal(root.get("name"), "John"));

session.beginTransaction();
int deletedCount = session.createQuery(deleteQuery).executeUpdate();
session.getTransaction().commit();

Updating Data using Criteria API

🔹 Equivalent SQL: UPDATE student SET age = 25 WHERE name = 'Alice';

CriteriaBuilder builder = session.getCriteriaBuilder();
CriteriaUpdate<Student> updateQuery = builder.createCriteriaUpdate(Student.class);
Root<Student> root = updateQuery.from(Student.class);

updateQuery.set("age", 25).where(builder.equal(root.get("name"), "Alice"));

session.beginTransaction();
int updatedCount = session.createQuery(updateQuery).executeUpdate();
session.getTransaction().commit();

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