Pao Ding Jie Niu, analyzing the knowledge system of Java Hibernate framework

php editor Youzi introduces: Pao Ding Jie Niu, analyzes the knowledge system of Java Hibernate framework, deeply discusses the core principles and key features of Hibernate framework, and helps readers better understand and use Hibernate technology.

1. Hibernate FrameworkOverview

The Hibernate framework is a persistence layer framework for Java development, which can map Java objects to relational database tables, thereby simplifying database operations. Hibernate uses object-oriented design ideas to map data in database tables into Java objects, and provides a rich api to operate these objects. The advantages of the Hibernate framework are:

• Simplify database operations: Hibernate provides a rich API to operate the database, simplifying the code writing of database operations.
• Improve development efficiency: Hibernate can automatically generate the structure of the database table and provide rich query functions, improving development efficiency.
• Improve program performance: Hibernate uses a caching mechanism to improve program performance.
• Supports multiple databases: Hibernate supports multiple databases, such as Mysql, oracle, postgresql, etc.

2. Basic concepts of Hibernate framework

1. Entity class

The entity class is one of the most important concepts in the Hibernate framework. It is used to represent a row of records in a database table. Entity classes usually correspond to database tables one-to-one. The entity class contains the fields in the database table and the access methods to these fields.

2. Mapping file

Mapping files are used to describe the mapping relationship between entity classes and database tables. Mapping files are usually written in XML format and contain the correspondence between attributes in entity classes and database table fields.

3. Session Factory

Session factory is used to create session objects. The session object is used to operate the database. It can perform operations such as query, update, and delete.

4. Session object

The session object is used to operate the database. It can perform operations such as query, update, and delete. The session object is threadsafe, and it can be used by multiple threads at the same time.

5. Transaction

Transactions are used to ensure the atomicity, consistency, isolation and durability of database operations. A transaction can contain multiple operations, and if one of the operations fails, the entire transaction is rolled back.

3. How to use the Hibernate framework

1. Import dependencies

To use the Hibernate framework in project, you first need to import Hibernate dependencies. In the Maven project, you can add the following dependencies:

<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>5.4.2.Final</version>
</dependency>

2. Create entity class

Create an entity class, which contains the fields in the database table and the access methods to these fields.

@Entity
public class User {

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

private String username;

private String passWord;

// getter and setter methods
}

3. Create mapping file

Create a mapping file. The mapping file is usually written in XML format and contains the correspondence between the attributes in the entity class and the database table fields.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "Http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
<class name="com.example.demo.User">
<id name="id">
<generator class="identity"/>
</id>
<property name="username"/>
<property name="password"/>
</class>
</hibernate-mapping>

4. Create session factory

Create a session factory, which is used to create session objects.

SessionFactory sessionFactory = new Configuration()
.configure("hibernate.cfg.xml") // 加载映射文件
.buildSessionFactory();

5. Create session object

Create a session object, which is used to operate the database.

Session session = sessionFactory.openSession();

6. Perform operations

You can use the session object to perform operations such as query, update, delete, etc.

// 查询所有用户
List<User> users = session.createQuery("from User", User.class).list();

// 保存一个用户
User user = new User();
user.setUsername("John");
user.setPassword("123456");
session.save(user);

// 提交事务
session.getTransaction().commit();

7. Close the session object

Close the session object.

session.close();

8. Close the session factory

Close the session factory.

sessionFactory.close();

IV. Summary

The Hibernate framework is a powerful and easy-to-use persistence layer framework. It maps Java objects to relational database tables, simplifying database operations. This article provides a detailed analysis of the knowledge system of the Hibernate framework to help readers deeply understand the working principles and usage of Hibernate.

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