Hibernate Query Language INSERT, UPDATE, SELECT and DELETE Example

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In this tutorial, we will demonstrate how to perform basic CRUD (Create, Read, Update, Delete) operations using Hibernate Query Language (HQL) with a Product entity. We will create a simple application to manage Product entities with Hibernate.

Introduction to HQL (Hibernate Query Language)

What is HQL?

HQL (Hibernate Query Language) is an object-oriented query language similar to SQL, but it is designed for querying entities stored in a relational database using the Hibernate ORM framework. HQL allows you to write queries in a way that is closely aligned with the object model of the application rather than the relational model of the database.

Key Points of HQL:

  • Object-Oriented: HQL queries are written in terms of the object model and the entities defined in the application, not the database tables and columns.
  • Database Independent: HQL is designed to be database-independent, allowing you to switch databases without changing your queries.
  • Powerful and Flexible: HQL supports all CRUD operations and provides powerful features like joins, aggregations, and subqueries.

Basic Syntax of HQL:

  • SELECT Queries: Used to retrieve data from the database. 
    SELECT s FROM Student s WHERE s.firstName = 'Ramesh'
  • INSERT Queries: Not directly supported, but can be achieved using entity manipulation.
  • UPDATE Queries: Used to update existing records. 
    UPDATE Student s SET s.email = '[email protected]' WHERE s.id = 1
  • DELETE Queries: Used to delete records. 
    DELETE FROM Student s WHERE s.id = 1

Example of HQL:

Here's a simple example demonstrating the usage of HQL to fetch all students with a specific first name:

String hql = "FROM Student S WHERE S.firstName = :firstName";
Query query = session.createQuery(hql);
query.setParameter("firstName", "Ramesh");
List results = query.list();

In this example:

  • FROM Student S specifies that we are querying the Student entity.
  • WHERE S.firstName = :firstName applies a filter to only fetch students with the first name "Ramesh".
  • session.createQuery(hql) creates an HQL query from the session.
  • query.setParameter("firstName", "Ramesh") sets the parameter value.
  • query.list() executes the query and returns the results as a list.

HQL provides a powerful way to interact with your database through the object-oriented model of your application, making it easier to write and maintain queries.

Prerequisites

Before we start, ensure you have the following:

  • Java Development Kit (JDK) installed
  • Apache Maven installed
  • An IDE (such as IntelliJ IDEA, Eclipse, or VS Code) installed

Step 1: Setting Up the Hibernate Project

1.1 Create a Maven Project

  1. Open your IDE and create a new Maven project.

  2. Configure the pom.xml file:

Add the following dependencies to your pom.xml:

<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>hibernate-example</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <dependency>
            <groupId>org.hibernate.orm</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>6.4.0.Final</version>
        </dependency>
        <dependency>
            <groupId>org.hibernate.orm</groupId>
            <artifactId>hibernate-hikaricp</artifactId>
            <version>6.4.0.Final</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.32</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
            <version>1.7.32</version>
        </dependency>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <version>2.1.210</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.1</version>
                <configuration>
                    <source>17</source>
                    <target>17</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

1.2 Configure Hibernate

Create a file named hibernate.cfg.xml in the src/main/resources directory with the following content:

<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <property name="hibernate.dialect">org.hibernate.dialect.H2Dialect</property>
        <property name="hibernate.connection.driver_class">org.h2.Driver</property>
        <property name="hibernate.connection.url">jdbc:h2:mem:testdb;DB_CLOSE_DELAY=-1</property>
        <property name="hibernate.connection.username">sa</property>
        <property name="hibernate.connection.password"></property>
        <property name="hibernate.hbm2ddl.auto">update</property>
        <property name="hibernate.show_sql">true</property>
        <property name="hibernate.format_sql">true</property>
    </session-factory>
</hibernate-configuration>

1.3 Create the Product Entity

Create a Product class in the com.example.hibernateexample.model package:

package com.example.hibernateexample.model;

import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;

@Entity
public class Product {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private double price;

    // Getters and Setters
    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }
}

1.4 Create the Hibernate Utility Class

Create a HibernateUtil class in the com.example.hibernateexample.util package:

package com.example.hibernateexample.util;

import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {

    private static final SessionFactory sessionFactory = buildSessionFactory();

    private static SessionFactory buildSessionFactory() {
        try {
            Configuration configuration = new Configuration();
            configuration.configure("hibernate.cfg.xml");
            return configuration.buildSessionFactory(new StandardServiceRegistryBuilder()
                    .applySettings(configuration.getProperties()).build());
        } catch (Throwable ex) {
            System.err.println("Initial SessionFactory creation failed." + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }

    public static void shutdown() {
        getSessionFactory().close();
    }
}

Step 2: Performing CRUD Operations with HQL

2.1 INSERT Operation

Create a ProductDao class in the com.example.hibernateexample.dao package to handle database operations:

package com.example.hibernateexample.dao;

import com.example.hibernateexample.model.Product;
import com.example.hibernateexample.util.HibernateUtil;
import org.hibernate.Session;
import org.hibernate.Transaction;

public class ProductDao {

    public void saveProduct(Product product) {
        Transaction transaction = null;
        try (Session session = HibernateUtil.getSessionFactory().openSession()) {
            transaction = session.beginTransaction();
            session.save(product);
            transaction.commit();
        } catch (Exception e) {
            if (transaction != null) {
                transaction.rollback();
            }
            e.printStackTrace();
        }
    }
}

2.2 SELECT Operation

Add a method to the ProductDao class to retrieve all products:

import java.util.List;
import org.hibernate.query.Query;

public List<Product> getProducts() {
    try (Session session = HibernateUtil.getSessionFactory().openSession()) {
        Query<Product> query = session.createQuery("from Product", Product.class);
        return query.list();
    }
}

2.3 UPDATE Operation

Add a method to the ProductDao class to update a product:

public void updateProduct(Product product) {
    Transaction transaction = null;
    try (Session session = HibernateUtil.getSessionFactory().openSession()) {
        transaction = session.beginTransaction();
        session.update(product);
        transaction.commit();
    } catch (Exception e) {
        if (transaction != null) {
            transaction.rollback();
        }
        e.printStackTrace();
    }
}

2.4 DELETE Operation

Add a method to the ProductDao class to delete a product:

public void deleteProduct(Long id) {
    Transaction transaction = null;
    try (Session session = HibernateUtil.getSessionFactory().openSession()) {
        transaction = session.beginTransaction();
        Product product = session.get(Product.class, id);
        if (product != null) {
            session.delete(product);
            System.out.println("Product is deleted");
        }
        transaction.commit();
    } catch (Exception e) {
        if (transaction != null) {
            transaction.rollback();
        }
        e.printStackTrace();
    }
}

Step 3: Testing the CRUD Operations

Create a Main class in the com.example.hibernateexample package to test the CRUD operations:

package com.example.hibernateexample;

import com.example.hibernateexample.dao.ProductDao;
import com.example.hibernateexample.model.Product;

import java.util.List;

public class Main {
    public static void main(String[] args) {
        ProductDao productDao = new ProductDao();

        // Insert a product
        Product product1 = new Product();
        product1.setName("Product 1");
        product1.setPrice(100.00);
        productDao.saveProduct(product1);

        // Insert another product
        Product product2 = new Product();
        product2.setName("Product 2");
        product2.setPrice(200.00);
        productDao.saveProduct(product2);

        // Select all products
        List<Product> products = productDao.getProducts();
        products.forEach(p -> System.out.println(p.getName() + " - " + p.getPrice()));

        // Update a product
        product1.setPrice(150.00);
        productDao.updateProduct(product1);

        // Select all products again
        products = productDao.getProducts();
        products.forEach(p -> System.out.println(p.getName() + " - " + p.getPrice()));

        // Delete a product
        productDao.deleteProduct(product2.getId());

        // Select all products again


        products = productDao.getProducts();
        products.forEach(p -> System.out.println(p.getName() + " - " + p.getPrice()));
    }
}

Conclusion

In this tutorial, we set up a simple Hibernate project using Maven and demonstrated how to perform basic CRUD operations using Hibernate Query Language (HQL). We created a Product entity and a ProductDao class to handle database operations. We tested the CRUD operations in a Main class. By following this structure, you can extend and customize the application as needed.

Comments

  1. T6 October 2019 at 04:46

    I don't understand the insert statement. What if I have a Student passed in as a parameter? How do we pass those values to the query?

    ReplyDelete

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