Introduction To Querying | Querying

What is Querying?

Querying is the process of retrieving data from a database. In Hibernate, querying is an essential aspect that allows developers to perform searches and retrieve objects from the database using HQL (Hibernate Query Language), Criteria API, or native SQL queries.

Hibernate Query Language (HQL)

HQL is an object-oriented query language, similar to SQL but operates on the entity objects rather than the database tables. HQL queries are translated into SQL by Hibernate at runtime.

Example of HQL

Consider an entity class named Employee. To retrieve all employees, you can use:

String hql = "FROM Employee";

Criteria API

The Criteria API is a more programmatic way to build queries in Hibernate. It allows for dynamic query building and is especially useful when you need to build complex queries.

Example of Criteria API

To retrieve all employees using Criteria, you can write:

CriteriaBuilder criteriaBuilder = session.getCriteriaBuilder();

CriteriaQuery criteriaQuery = criteriaBuilder.createQuery(Employee.class);

criteriaQuery.from(Employee.class);

List employees = session.createQuery(criteriaQuery).getResultList();

Native SQL Queries

Native SQL queries allow you to execute SQL statements directly against the database. This is useful when you need to perform database-specific operations that are not easily achievable using HQL or Criteria API.

Example of Native SQL

To perform a native SQL query, you can do:

String sql = "SELECT * FROM Employee";

List employees = session.createNativeQuery(sql, Employee.class).getResultList();

Conclusion

Querying in Hibernate is a powerful mechanism that provides multiple ways to retrieve data from the database. Whether you choose HQL, Criteria API, or Native SQL, Hibernate offers flexibility to cater to the needs of your application. Understanding these querying methods is crucial for effective data manipulation in Hibernate.

Introduction to Querying in Hibernate