Explain HQL and it’s benefits
Hibernate Query Language (HQL) is an object-oriented query language, similar to SQL, designed for Hibernate. Hibernate Query Language allows you to query and manipulate data from the database in an object-oriented way, using the entity objects rather than table names and columns.
Benefits of Hibernate Query Language:
1. Object-Oriented : Hql uses the entity objects and their properties instead of database tables and columns. This makes it more intuitive and easier to use for developers familiar with object-oriented programming.
2. Database Independence : HQL abstracts the database-specific details. The same Hibernate Query Language query can work across different databases without modification.
3. Automatic Table Join Handling : Hibernate Query Language can automatically handle joins based on the relationships defined in the entities, reducing the complexity of writing join queries.
4. Supports Polymorphic Queries : HQL can query not just the specific class but also its subclasses, making it useful for inheritance mapping strategies.
5. Caching : Hql can take advantage of Hibernate’s caching mechanisms, which can significantly improve the performance of query operations.

Table of Contents
Example in Java using Hibernate Query Language
Consider two entities: Employee and Department.
Entities Definition:
1. Employee.java
java
@Entity
@Table(name = "employee")
public class Employee {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Column(name = "name")
private String name;
@ManyToOne
@JoinColumn(name = "department_id")
private Department department;
// Getters and Setters
}
2. Department.java
java
@Entity
@Table(name = "department")
public class Department {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Column(name = "name")
private String name;
// Getters and Setters
}
HQL Example:
1. Selecting All Employees
java
String hql = "FROM Employee";
Query query = session.createQuery(hql);
List<Employee> employees = query.list();
for (Employee employee : employees) {
System.out.println(employee.getName());
}
2. Selecting Employees by Department Name
java
String hql = "FROM Employee e WHERE e.department.name = :departmentName";
Query query = session.createQuery(hql);
query.setParameter("departmentName", "HR");
List<Employee> employees = query.list();
for (Employee employee : employees) {
System.out.println(employee.getName());
}