Hibernate - 无法定位实体描述符

Question

我是 Java（和 Hibernate）新手，为了学习 Java，我想使用数据库创建具有简单 CRUD 操作的普通 Java 应用程序。我找到了有关设置休眠的文章，因此我按照它进行操作，结果如下：

import jakarta.persistence.*;
@Entity
@Table(name = "student")
public class Student {

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

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

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

    // constructor
    // getters and setters

}

hibernate.cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "https://hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <property name="hibernate.connection.driver_class">org.postgresql.Driver</property>
        <property name="hibernate.connection.url">jdbc:postgresql://localhost:5432/db_student</property>
        <property name="hibernate.connection.username">my username</property>
        <property name="hibernate.connection.password">my password</property>

        <property name="hibernate.connection.pool_size">1</property>

        <property name="hibernate.current_session_context_class">thread</property>

        <mapping class="com.model.Student"/>
    </session-factory>
</hibernate-configuration>

HibernateUtil.java

public class HibernateUtil {

    private static SessionFactory sessionFactory;

    private static SessionFactory sessionJavaConfigFactory;

    private static SessionFactory buildSessionFactory() {
        try {
            // Create the SessionFactory from hibernate.cfg.xml
            Configuration configuration = new Configuration();
            configuration.configure("hibernate.cfg.xml");
            System.out.println("Hibernate Annotation Configuration loaded");

            ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build();
            System.out.println("Hibernate Annotation serviceRegistry created");

            SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);

            return sessionFactory;
        }
        catch (Throwable ex) {
            System.err.println("Initial SessionFactory creation failed." + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }

    private static SessionFactory buildSessionJavaConfigFactory() {
        try {
            Configuration configuration = new Configuration();

            //Create Properties, can be read from property files too
            Properties props = new Properties();
            props.put("hibernate.connection.driver_class", "org.postgresql.Driver");
            props.put("hibernate.connection.url", "jdbc:postgresql://localhost:5432/db_student");
            props.put("hibernate.connection.username", "my username");
            props.put("hibernate.connection.password", "my password");
            props.put("hibernate.current_session_context_class", "thread");

            configuration.setProperties(props);

            ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build();
            System.out.println("Hibernate Java Config serviceRegistry created");

            SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);

            return sessionFactory;
        }
        catch (Throwable ex) {
            System.err.println("Initial SessionFactory creation failed." + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static SessionFactory getSessionFactory() {
        if(sessionFactory == null) sessionFactory = buildSessionFactory();
        return sessionFactory;
    }

    public static SessionFactory getSessionJavaConfigFactory() {
        if(sessionJavaConfigFactory == null) sessionJavaConfigFactory =   buildSessionJavaConfigFactory();
        return sessionJavaConfigFactory;
    }
}

在 Main.java 中我放入：

public class Main {
    public static void main(String[] args) {
        Session session = HibernateUtil.getSessionFactory().openSession();
        Transaction transaction = session.beginTransaction();
        
        Student fetchedStudent = session.get(Student.class, 1);
        if (fetchedStudent != null) {
            System.out.println("Student found: " + fetchedStudent.getFirstname());
        } else {
            System.out.println("Student not found.");
        }
        transaction.commit();
        session.close();
    }
}

但我不断收到错误：
线程“main”中的异常org.hibernate.UnknownEntityTypeException：无法找到实体描述符：com.model.Student

我发现问题可能出在使用较旧的 hibernate 版本，但就我而言，在我的 pom.xml 中我有：

 <dependency>
        <groupId>org.hibernate.orm</groupId>
        <artifactId>hibernate-core</artifactId>
        <version>6.6.1.Final</version>
    </dependency>

Answer 1

这是因为 Hibernate 不知道您的

Student

实体。

自 Hibernate 5 起，

Configuration.configure()

方法已被破坏。如果您想通过

hibernate.cfg.xml

添加映射，请使用 MetadataSources:

StandardServiceRegistry registry = new StandardServiceRegistryBuilder().configure().build();
SessionFactory sessionFactory = new MetadataSources(registry).buildMetadata().buildSessionFactory();

或者您可以简单地使用

Configuration.addAnnotatedClass()

注册您的实体

configuration.addAnnotatedClass(Student.class);