package hibernate.test;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="user")
public class User {
	
	
	@Id
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	@Column(name="id")
	private int uId;
	
    @Column(name="first_name")
	private String uName;

	public int getuId() {
		return uId;
	}

	public void setuId(int uId) {
		this.uId = uId;
	}

	public String getuName() {
		return uName;
	}

	public void setuName(String uName) {
		this.uName = uName;
	}

}

	public static void main(String[] args) {

		UserDao dao = new UserDao();
		User user = new User();
		user.setuName("Oleg");
		dao.addApplicant(user);

	}

public class UserDao {

	public Long addApplicant(User user) {
        Session session = HibernateUtil.getSessionFactory().getCurrentSession();
        session.beginTransaction();
        Long result = (Long) session.save(user);
        session.getTransaction().commit();
        return result;
    }
}

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD//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://127.0.0.1:3306/test</property>
        <property name="connection.username">root</property>
        <property name="connection.password">root</property>

      <!-- SQL dialect -->
        <property name="dialect">org.hibernate.dialect.MySQLInnoDBDialect</property>

      <!-- JDBC connection pool (use the built-in) -->
        <property name="connection.pool_size">2</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>

      <!-- Echo all executed SQL to stdout -->
        <property name="show_sql">true</property>
        
        <mapping class="hibernate.test.User"/>

    </session-factory>

</hibernate-configuration>

log4j:WARN No appenders could be found for logger (org.hibernate.type.BasicTypeRegistry).
log4j:WARN Please initialize the log4j system properly.
Hibernate: insert into user (first_name) values (?)
Exception in thread "main" org.hibernate.exception.GenericJDBCException: could not insert: [hibernate.test.User]
	at org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:140)
	at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:128)
	at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66)
	at org.hibernate.id.insert.AbstractReturningDelegate.performInsert(AbstractReturningDelegate.java:63)
	at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2346)
	at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2853)
	at org.hibernate.action.EntityIdentityInsertAction.execute(EntityIdentityInsertAction.java:71)
	at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:273)
	at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:320)
	at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:203)
	at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:129)
	at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:210)
	at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:56)
	at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:195)
	at org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:50)
	at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:93)
	at org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:713)
	at org.hibernate.impl.SessionImpl.save(SessionImpl.java:701)
	at org.hibernate.impl.SessionImpl.save(SessionImpl.java:697)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.hibernate.context.ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:345)
	at $Proxy8.save(Unknown Source)
	at hibernate.test.UserDao.addApplicant(UserDao.java:10)
	at hibernate.test.UserTest.main(UserTest.java:15)
Caused by: java.sql.SQLException: Field 'id' doesn't have a default value
	at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2975)
	at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1600)
	at com.mysql.jdbc.ServerPreparedStatement.serverExecute(ServerPreparedStatement.java:1125)
	at com.mysql.jdbc.ServerPreparedStatement.executeInternal(ServerPreparedStatement.java:677)
	at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1357)
	at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1274)
	at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1259)
	at org.hibernate.id.IdentityGenerator$GetGeneratedKeysDelegate.executeAndExtract(IdentityGenerator.java:93)
	at org.hibernate.id.insert.AbstractReturningDelegate.performInsert(AbstractReturningDelegate.java:56)
	... 23 more