java - Hibernate 5 :- org.hibernate.MappingException: Unknown entity

Question

I am getting the error message org.hibernate.MappingException: Unknown entity when i am trying to integrate hibernate 5.0 with mysql

This seems to be an issue with hibernate5.0.0 and 5.0.1 . This works fine with hibernate 4.3.9

Maven dependices

<dependency>
    <groupId>org.hibernate</groupId>
        <artifactId>hibernate-core</artifactId>
        <version>5.0.0.Final</version>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.36</version>
</dependency>

hibernate.cfg.xml

<session-factory>

    <!-- Database connection settings -->
    <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
    <property name="connection.url">jdbc:mysql://localhost:3307/SampleDB
    </property>
    <property name="connection.username">root</property>
    <property name="connection.password"></property>

    <!-- JDBC connection pool (use the built-in) -->
    <property name="connection.pool_size">1</property>
    <property name="dialect">org.hibernate.dialect.MySQLDialect</property>

    <!-- Echo all executed SQL to stdout -->
    <property name="show_sql">true</property>

    <!-- Drop and re-create the database schema on startup -->
    <property name="hbm2ddl.auto">create</property>

    <mapping class="UserA.User"></mapping>

</session-factory>

HibernateMain.java code

package UserA;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.mapping.Map;
import org.hibernate.metadata.ClassMetadata;
import org.hibernate.persister.entity.EntityPersister;
import org.hibernate.service.ServiceRegistry;

public class HibernateMain {

    public static void main(String[] args) {

        Configuration configuration = new Configuration();
        configuration.configure();
        ServiceRegistry sr = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build();

        SessionFactory sf = configuration.buildSessionFactory(sr);




        User user1 = new User();
        user1.setUserName("Arpit");
        user1.setUserMessage("Hello world from arpit");
        user1.setUserId(22);

        Session ss = sf.openSession();
        ss.beginTransaction();
        // saving objects to session
        ss.save(user1);
        ss.getTransaction().commit();
        ss.close();

    }

}

User.java

package UserA;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;

@Entity(name="User_table")
public class User {
    @Id
    int userId;
    @Column(name = "User_Name")
    String userName;

    @Column(name = "User_Message")
    String userMessage;

    public int getUserId() {
        return userId;
    }

    public void setUserId(int userId) {
        this.userId = userId;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getUserMessage() {
        return userMessage;
    }

    public void setUserMessage(String userMessage) {
        this.userMessage = userMessage;
    }

}

Answer 1

I have fixed the same issue with Hibernate 5. There is a problem in this code

Configuration configuration = new Configuration();
configuration.configure();

ServiceRegistry sr = new StandardServiceRegistryBuilder().applySettings(
    configuration.getProperties()).build();

SessionFactory sf = configuration.buildSessionFactory(sr);

This code works fine for Hibernate 4.3.5, but the same code has the same issue for Hibernate 5.

When you do configuration.buildSessionFactory(sr), using Hibernate 5, Configuration losts all information about mapping that gets by call configuration.configure().

Solution

To fix the issue, if you use standard configuration files hibernate.cfg.xml and hibernate.properties, you can create the session factory by this way (without ServiceRegistry)

SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();

Loading properties

If you have properties in a file other then hibernate.properties, you can build session factory using StandardServiceRegistryBuilder (anyway, if you have hibernate.properties and other file, it will be loaded both)

To load properties as a resource

ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().
    configure().loadProperties("hibernate-h2.properties").build();
SessionFactory sf = new Configuration().buildSessionFactory(serviceRegistry);  

You need to have hibernate-h2.properties in the class path (root of the sources folder, resources folder). You can specify a path from the root source folder too /com/github/xxx/model/hibernate-h2.properties.

To load properties from a path in the file system

File propertiesPath = new File("some_path");
ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().
    configure().loadProperties(propertiesPath).build();
SessionFactory sf = new Configuration().buildSessionFactory(serviceRegistry);

You can find an example console application using this approach here fluent-hibernate-mysql. It uses a utility class to build the session factory from the fluent-hibernate library.

Incorrect Hibernate 5 tutorial

There is an incorrect example in Hibernate 5 tutorial 1.1.6. Startup and helpers. It uses this code

 return new Configuration().configure().buildSessionFactory(
                new StandardServiceRegistryBuilder().build() );

It doesn't do a proper configuration.