Hibernate framework study notes: from concept to practice

The Hibernate framework simplifies the process of interacting with the database in Java applications, involving the following concepts: entities (POJO represents database tables), sessions (database interaction), queries (retrieving data), mapping (association of classes and tables), transactions (Ensuring data consistency). Practical cases demonstrate the steps to create database tables, entity classes, Hibernate configuration files, and use the Hibernate API to perform basic database operations.

Hibernate framework study notes: from concept to practice

Introduction

Hibernate It is a lightweight, high-performance, open source Java persistence framework. It simplifies the process of managing and persisting objects to a database in Java applications.

Basic concepts

• Entity: Represents a table in the database. They are represented through POJOs (Plain Old Java Objects).
• Session: A single interaction with the database.
• Query: Object used to retrieve data from the database.
• Mapping: Associate Java classes with database tables.
• Transaction: Guarantee the atomicity and consistency of database operations.

Practical case:

We will create a simple application to demonstrate the basic operation of Hibernate.

Setup

You will need:

• Java Development Kit (JDK)
• Maven or Gradle build tool
• MySQL Database and Connector

Database Table

Create a database table named User:

CREATE TABLE User (
    id INT NOT NULL AUTO_INCREMENT,
    name VARCHAR(255) NOT NULL,
    email VARCHAR(255) NOT NULL,
    PRIMARY KEY (id)
);

Entity Class

Create the entity class used to map the User table User.java:

@Entity
@Table(name = "User")
public class User {

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

    // Getters and setters
}

Hibernate Configuration File

Create a Hibernate configuration file named hibernate.cfg.xml:

<?xml version="1.0"?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
    <session-factory>
        <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/hibernate</property>
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.connection.password">password</property>
        <property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property>
        <mapping class="com.example.model.User" />
    </session-factory>
</hibernate-configuration>

Java Operation

Perform Hibernate operations in the Main.java class:

public class Main {

    public static void main(String[] args) {
        // 创建SessionFactory
        SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();

        // 打开一个新的会话
        Session session = sessionFactory.openSession();

        // 开始一个事务
        Transaction transaction = session.beginTransaction();

        // 创建一个新的User实体
        User user = new User();
        user.setName("John");
        user.setEmail("john@example.com");

        // 保存实体
        session.save(user);

        // 提交事务
        transaction.commit();

        // 关闭会话
        session.close();
    }
}

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