Come and learn about Hibernate ORM, an object-relational mapping framework for the Java programming language

Table of contents

1. What is Hibernate ORM

2. How to use Hibernate ORM

3. The advantages and functions of Hibernate ORM

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1. What is Hibernate ORM

Hibernate is a popular open-source object-relational mapping (ORM) framework for persisting objects in Java applications to relational databases. It provides an easy and efficient way to handle database access and manipulation, allowing developers to focus more on business logic without worrying about database details. This article will introduce Hibernate ORM in detail.

The Hibernate ORM framework was created by Gavin King et al. in 2001 when it was called the "Hibernate Object/Relational Mapping" framework. Over the past few years, Hibernate has become one of the most popular ORM frameworks, thanks to its widespread use and community support.

Key features of the Hibernate ORM framework include:

1. Object-relational mapping: Hibernate can directly map Java objects to relational database tables, and automatically complete database interaction through ORM technology. This means that developers do not need to write SQL statements, nor do they need to understand the details of the database table structure.

2. Database query: Hibernate provides a rich query API that enables developers to easily perform various database queries. These queries can be implemented through HQL (Hibernate Query Language), Criteria API and Native SQL statements.

3. Transaction management: Hibernate supports transaction management, which can ensure that all database operations are performed in an atomic unit when creating, updating or deleting objects. This ensures data integrity and consistency.

4. Cache management: Hibernate provides a caching mechanism that helps developers reduce the number of interactions with the database and improve application performance. Hibernate caching includes a first-level cache and a second-level cache, which can be easily configured and customized.

5. Transparency: Another major advantage of the Hibernate ORM framework is its transparency. This means that developers can program using Java objects without having to deal directly with SQL statements or database table structures. Hibernate will automatically map the Java objects to the database table structure and perform the necessary conversions when needed.

The following is a simple Hibernate ORM framework example that demonstrates how to persist Java objects into a relational database.

First, you need to add Hibernate and JDBC driver dependencies to your application. Here is an example Maven dependency:

<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-core</artifactId>
    <version>5.5.6.Final</version>
</dependency>

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.26</version>
</dependency>

Next, you can use Hibernate's relevant annotations (such as @Entity, @Column, etc.) to mark Java entity classes and specify how they are mapped to database tables. Here is sample code:

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

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

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

    // getters and setters for all fields
}

In this example, the User class is annotated @Entity to indicate that it is a Hibernate entity class and can be mapped to a database table named "users". It also contains id, username and password properties annotated as @Id, @GeneratedValue and @Column to specify how they map to database table fields.

Finally, you can use Hibernate's Session API to perform database operations such as inserting new user records.

 

2. How to use Hibernate ORM

Hibernate ORM is an ORM (Object Relational Mapping) framework written in Java that provides a way to map between objects in a Java application and a relational database. With Hibernate, developers can use object-oriented methods to operate relational databases and reduce the amount of code that uses JDBC directly. Following is a simple Hibernate ORM example that demonstrates how to use Hibernate ORM to map Java objects to relational database tables.

First, you need to add the necessary dependencies and configuration files to your web application. Here is an example built on Maven:

<dependency>
   <groupId>org.hibernate</groupId>
   <artifactId>hibernate-core</artifactId>
   <version>5.4.32.Final</version>
</dependency>

<dependency>
   <groupId>mysql</groupId>
   <artifactId>mysql-connector-java</artifactId>
   <version>8.0.23</version>
</dependency>

Next, you can create a Hibernate entity class, such as the Person class, that represents a table in the database. Here is sample code:

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

@Entity
public class Person {

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

   private String name;
   private int age;

   // getters and setters for id, name, and age

}

In this example, the Person class is annotated @Entity to indicate that it is a Hibernate entity class. It contains three fields: id, name and age, and corresponding getter and setter methods. The id field is annotated as @Id, and the @GeneratedValue strategy is specified as IDENTITY, indicating that it is an auto-increasing primary key.

Finally, you can create a Hibernate session factory object and use it to manipulate database tables. Here is sample code:

import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {

   private static SessionFactory sessionFactory = buildSessionFactory();

   private static SessionFactory buildSessionFactory() {
       try {
           Configuration configuration = new Configuration();
           configuration.configure("hibernate.cfg.xml");
           return configuration.buildSessionFactory();
       }
       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();
   }

}

In this example, the HibernateUtil class contains a buildSessionFactory() method that uses the hibernate.cfg.xml configuration file to build a Hibernate session factory object. The hibernate.cfg.xml file contains information about connecting to the database, such as the database URL, user name, and password. The getSessionFactory() method returns the Hibernate session factory object, which can be shared across the application. Finally, the shutdown() method closes the Hibernate session factory object.

Through the above steps, you can now use Hibernate ORM to map Java objects to relational database tables and perform operations. Common operations include inserting data, querying data, updating data, and deleting data. Here is some sample code:

Session session = HibernateUtil.getSessionFactory().getCurrentSession();
session.beginTransaction();

Person person = new Person();
person.setName("John");
person.setAge(25);

session.save(person);

session.getTransaction().commit();

This sample code creates a new Person object, sets its name and age, and saves it to the database using a Hibernate session. The beginTransaction() method starts a transaction, the save() method saves the Person object to the database, and the getTransaction().commit() method commits the transaction. You can also use other Hibernate methods to achieve more complex operations.

In summary, Hibernate ORM is an ORM framework that provides mapping between objects in Java applications and relational databases. By using Hibernate ORM, developers can use an object-oriented approach to manipulating relational databases and reduce the amount of code that uses JDBC directly. The above is a simple example of Hibernate ORM, which demonstrates how to map Java objects to relational database tables and perform operations.

 

3. The advantages and functions of Hibernate ORM

Hibernate ORM is an object-relational mapping framework for the Java programming language, which provides a way to map Java classes to relational database tables, and operate the database in an object-oriented manner . Hibernate ORM has the following advantages:

1. Simplified data persistence: Compared with traditional JDBC, Hibernate ORM abstracts many details of data persistence, enabling developers to perform data operations without manually writing complex SQL statements.

2. Highly customizable: Hibernate ORM allows the establishment of a complete relationship between entities, supports inheritance and polymorphism, and also provides various configuration options to meet various business needs.

3. Transparency: When using Hibernate ORM, developers can fully rely on the object model without having to care about the underlying database details. Hibernate ORM is responsible for handling all data operations, including reading and writing data from the database.

4. Improve performance: Hibernate ORM uses caching technology, which can reduce the number of database accesses and improve performance. In addition, Hibernate ORM also has a transaction management function, which can ensure the security and integrity of data.

5. Portability: Hibernate ORM is built on the standard Java Persistence API (JPA), which can be easily integrated with other JPA implementations and seamlessly switched between different databases.

Benefits of using Hibernate ORM :

1. Improve development efficiency: Hibernate ORM simplifies the complexity of data persistence, enabling developers to implement business logic faster.

2. Reduce errors: Hibernate ORM provides a type-safe query method, and can check syntax errors at compile time, thereby reducing code errors.

3. Improve application scalability: Using Hibernate ORM, developers can easily make data model and database schema changes, making the application more scalable.

4. Improve code readability: Hibernate ORM uses an object-oriented approach to data manipulation, which makes the code easier to understand and maintain.

In conclusion, Hibernate ORM is a very powerful ORM framework that helps developers achieve data persistence more easily. Its abstraction level is higher than that of JDBC, which simplifies the process of data persistence. It is highly customizable, portable, and has performance advantages, making it suitable for enterprise-level applications that need to handle large amounts of database access.