Hibernate Example using JPA and MySQL

Let's walk through a simple example of setting up a Hibernate project with JPA (Java Persistence API) and MySQL.

1. Setup

Dependencies: You'll need the following Maven dependencies:

<!-- MySQL JDBC Driver -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.26</version>  <!-- Use the latest version -->
</dependency>

<!-- Hibernate ORM and JPA -->
<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-core</artifactId>
    <version>5.5.6.Final</version>  <!-- Use the latest version -->
</dependency>

<!-- JPA API -->
<dependency>
    <groupId>javax.persistence</groupId>
    <artifactId>javax.persistence-api</artifactId>
    <version>2.2</version>
</dependency>

2. Entity Creation

Let's create a simple Book entity.

@Entity
@Table(name = "book")
public class Book {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "title")
    private String title;

    @Column(name = "author")
    private String author;

    // Constructors, getters, setters...
}

3. Persistence Configuration

Create a persistence.xml file under src/main/resources/META-INF/.

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.2"
             xmlns="http://xmlns.jcp.org/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
             http://xmlns.jcp.org/xml/ns/persistence/persistence_2_2.xsd">
    <persistence-unit name="book_pu">
        <!-- Entity classes -->
        <class>com.example.Book</class>

        <!-- Provider and DataSource -->
        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
        <properties>
            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL8Dialect"/>
            <property name="hibernate.hbm2ddl.auto" value="update"/>
            <property name="hibernate.show_sql" value="true"/>
            <property name="javax.persistence.jdbc.driver" value="com.mysql.cj.jdbc.Driver"/>
            <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/test_db"/>
            <property name="javax.persistence.jdbc.user" value="root"/>
            <property name="javax.persistence.jdbc.password" value="password"/>
        </properties>
    </persistence-unit>
</persistence>

Note: Update the database connection details (URL, user, password) as per your MySQL setup.

4. CRUD Operations

You can perform CRUD operations using the EntityManager.

public class BookService {

    private EntityManagerFactory emf = Persistence.createEntityManagerFactory("book_pu");
    private EntityManager em = emf.createEntityManager();

    public Book addBook(String title, String author) {
        Book book = new Book();
        book.setTitle(title);
        book.setAuthor(author);

        em.getTransaction().begin();
        em.persist(book);
        em.getTransaction().commit();

        return book;
    }

    public Book findBook(Long id) {
        return em.find(Book.class, id);
    }

    // You can add update and delete methods in a similar fashion.
}

5. Running the Application

Here's a simple main class to add a book:

public class Main {

    public static void main(String[] args) {
        BookService bookService = new BookService();
        
        Book book = bookService.addBook("Hibernate in Action", "Christian Bauer");
        System.out.println("Book ID: " + book.getId());
        
        Book foundBook = bookService.findBook(book.getId());
        System.out.println("Found Book Title: " + foundBook.getTitle());
    }
}

When you run this, Hibernate will interact with MySQL using JPA, creating the book table (if it doesn't exist) and adding a new entry.

Remember, this is a basic example to get you started. In a real-world scenario, you'd integrate dependency injection, handle exceptions, and potentially integrate with a framework like Spring.

Hibernate JPA configuration with MySQL:

Description: Configure the persistence.xml file to set up the JPA configuration, including the database connection details for MySQL.

Code:

<!-- persistence.xml -->
<persistence-unit name="example-unit" transaction-type="RESOURCE_LOCAL">
    <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
    <properties>
        <property name="hibernate.connection.driver_class" value="com.mysql.cj.jdbc.Driver"/>
        <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/your_database"/>
        <property name="hibernate.connection.username" value="your_username"/>
        <property name="hibernate.connection.password" value="your_password"/>
        <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"/>
        <!-- other properties -->
    </properties>
</persistence-unit>

Creating entities for Hibernate JPA with MySQL:

Description: Define JPA entities that map to the corresponding MySQL database tables. Use annotations such as @Entity, @Table, @Id, etc.

Code:

@Entity
@Table(name = "employee")
public class Employee {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String firstName;
    private String lastName;

    // Getters and setters
}

Mapping relationships in Hibernate JPA with MySQL:

Description: Use JPA annotations such as @ManyToOne, @OneToMany, etc., to map relationships between entities in MySQL.

Code:

@Entity
@Table(name = "department")
public class Department {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;

    @OneToMany(mappedBy = "department")
    private List<Employee> employees;

    // Getters and setters
}

Hibernate JPA query examples for MySQL:

Description: Use JPQL (Java Persistence Query Language) or native queries to retrieve data from MySQL using Hibernate and JPA.

Code:

// JPQL example
TypedQuery<Employee> query = entityManager.createQuery("SELECT e FROM Employee e WHERE e.firstName = :firstName", Employee.class);
query.setParameter("firstName", "John");
List<Employee> employees = query.getResultList();