hbm2ddl Configuration and Name Annotations in Hibernate

Here we will learn about hbm2ddl Configuration in the hibernate configuration file (hibernate.cfg.xml). Actually hbm2ddl Configuration means hibernate mapping to create schema DDL (Data Definition Language).

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

Automatically validates or exports schema DDL to the database when the SessionFactory is created. With create-drop, the database schema will be dropped when the SessionFactory is closed explicitly.

<?xml version=”1.0″ encoding=”UTF-8″?>
<!DOCTYPE hibernate-configuration PUBLIC
“-//Hibernate/Hibernate Configuration DTD 3.0//EN”
“http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd”>

<hibernate-configuration>
    <session-factory>
        <!– Database connection settings –>
         <property name=”connection.driver_class”>com.mysql.jdbc.Driver</property>
         <property name=”connection.url”>jdbc:mysql://localhost:3306/hibernateDB</property>
         <property name=”connection.username”>username</property>
         <property name=”connection.password”>password</property>
         <property name=”connection.pool_size”>1</property>
         <!– SQL dialect –>
         <property name=”dialect”>org.hibernate.dialect.MySQLDialect</property>

        <!– Enable Hibernate’s automatic session context management –>
         <property name=”current_session_context_class”>thread</property>

        <!– Disable the second-level cache –>
         <property name=”cache.provider_class”>org.hibernate.cache.NoCacheProvider</property>

        <!– Show 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 files –>
       <mapping resource=”userdetails.hbm.xml”/>

     </session-factory>
</hibernate-configuration>

Here <property name=”hbm2ddl.auto”>create</property> means schema DDL created every time when SessionFactory Object is created.

UserDetails.java

package com.sdnext.hibernate.tutorial.dto;
import javax.persistence.Entity;
import javax.persistence.Column;
import javax.persistence.Id;
import javax.persistence.Table;
@Entity
@Table(name=”USER_TABLE”)
public class UserDetails
{
    @Id
    @Column(name=”USER_ID”)
    private int    userId;
   @Column(name=”USER_NAME”)
    private String userName;
    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;
    }
}

Now we run this example–

public class HibernateTestDemo {
    public static void main(String[] args)
    {
       //Create the model object
       UserDetails user1 = new UserDetails();
       UserDetails user2 = new UserDetails();
        user1.setUserId(1);
        user1.setUserName(“Dinesh Rajput”);
        user2.setUserId(2);
        user2.setUserName(“Anamika Rajput”);
   // Create Session Factory Object – using annotation configuration object
        SessionFactory sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();

//Create Session object from session factory object
Session session = sessionFactory.openSession();
        session.beginTransaction();

   //Use the session to save model objects
        session.save(user1);
        session.save(user2);
        session.getTransaction().commit();
        session.close();
       }
}

Run this example–

log4j:WARN No appenders could be found for logger (org.hibernate.cfg.annotations.Version).
log4j:WARN Please initialize the log4j system properly.
Hibernate: insert into USER_DETAILS ( USER_ID, USER_NAME) values (?, ?)
Hibernate: insert into USER_DETAILS ( USER_ID, USER_NAME) values (?, ?)

Now we get following table structure–

Again we running the following example-

public class HibernateTestDemo {
    public static void main(String[] args)
    {
       //Create the model object
       UserDetails user1 = new UserDetails();
       UserDetails user2 = new UserDetails();
        user1.setUserId(3);
        user1.setUserName(“Dev Rajput”);
        user2.setUserId(4);
        user2.setUserName(“Sweety Rajput”);
   // Create Session Factory Object – using annotation configuration object
        SessionFactory sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();

//Create Session object from session factory object
Session session = sessionFactory.openSession();
        session.beginTransaction();

   //Use the session to save model objects
        session.save(user1);
        session.save(user2);
        session.getTransaction().commit();
        session.close();
       }
}

Run this example–

Now we get the following table schema–

hbm2ddl Configuration and Name Annotations in Hibernate

Here we see that the previous data is destroyed when we are using in the hibernate.cfg.xml file using the following line.
<property name=”hbm2ddl.auto”>create</property>
Here
hbm2ddl.auto–>create -Always create new schema
hbm2ddl.auto–>update -Update existing schema
Now we are replacing above line with the <property name=”hbm2ddl.auto”>update</property>

Run this example–

Now we get the following table schema…

here we are looking the table USER_DETAILS only updated not again created.

Now in the Next Chapter we will learn about how to retrieve an object from database.

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