Single table inheritance strategy (or table per class hierarchy) with Oracle and Hibernate

Question

I'm using JEE6, Oracle database 11g and Hibernate. I'm trying to make the following inheritance work :

So WikiNotification and TodoNotification extend Notification. According to the single table inheritance strategy, there will be one and one only table for those three classes in the database.

Here is Notification :

@Entity
@ForceDiscriminator
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="NOTIFICATION_TYPE")
@Table(name="SMH_NOTIFICATION")
public class Notification extends AbstractPersistentObject{

    /**
     * 
     */
    private static final long serialVersionUID = -2313098389774322743L;

    @ManyToOne
    @JoinColumn(name="RECEIVER_ID", nullable=false)
    private Userprofile receiver;


    @Column(name="CLASSIFICATION",nullable = true, length=30)
    private String classification;

    @Column(name="DESCRIPTION", nullable = true, length=60)
    private String description;

    @Column(name="DEADLINE")
    @Temporal(TemporalType.DATE)
    private Date deadline;

This is WikiNotification :

//@Entity
@DiscriminatorValue("Wiki")
//@Table(name="SMH_NOTIFICATION")
//@Inheritance(discriminatorValue="Wiki")
public class WikiNotification extends Notification{

    /**
     * 
     */
    private static final long serialVersionUID = 5025643991898983953L;


    //the sender is the user who triggers the notification
    //for example, it can the one who modifies someone else's chapters
    @ManyToOne
    @JoinColumn(name="SENDER_ID", nullable=false)
    private Userprofile sender;

    //"0" if the owner has not accepted yet, "1" if he accepted
    @Column(name="ACCEPTED", length=1, nullable=false)
    private String accepted;

    //the notification type can be "delete", "submit" or "modify"
    @Column(name="NOTIFICATIONTYPE",length=20,nullable=false)
    private String notificationType;

    //mofications, deletions and submissions are related to this article chapter
    @ManyToOne
    @JoinColumn(name="ARTICLECHAPTER",nullable=false)
    private ArticleChapter chapter;

And TodoNotification :

//@Entity
@DiscriminatorValue("Todo")
//@Table(name="SMH_NOTIFICATION")
public class TodoNotification extends Notification{

    /**
     * 
     */
    private static final long serialVersionUID = 2482841237595539431L;

    @OneToOne
    @JoinColumn(name="TODO_ID", nullable=false)
    private ToDo todo;

What is not working so far is :

• I have one table 'SMH_NOTIFICATION' created but I don't see the discriminator column 'NOTIFICATION_TYPE' and I don't have the other columns for WikiNotification and TodoNotification :

• when I write @Entity in the classes WikiNotification and TodoNotification, I have two tables Wikinotification and Todonotification created in my database, which is not what I expected. There should be only one table 'SMH_NOTIFICATION'

I tried the following tutorials but it hasn't worked yet :

http://www.dineshonjava.com/p/implementing-inheritance-in-hibernate.html#.Vd71ZiXtlHw

https://en.wikibooks.org/wiki/Java_Persistence/Inheritance

http://www.thejavageek.com/2014/05/14/jpa-single-table-inheritance-example/

http://uaihebert.com/jpa-mini-book-first-steps-and-detailed-concepts/13/

http://viralpatel.net/blogs/hibernate-inheritence-table-per-hierarchy-mapping/

Edit:

When I make Notification an abstract class and when I add @Entity in WikiNotification and TodoNotification I get the following lines in Eclipse :

    INFO  27.08.15 14:45:34.996  org.hibernate.tool.hbm2ddl.DatabaseMetadata@getTableMetadata: table not found: TodoNotification
    INFO  27.08.15 14:45:35.001  org.hibernate.tool.hbm2ddl.DatabaseMetadata@getTableMetadata: table not found: WikiNotification
    INFO  27.08.15 14:45:35.007  org.hibernate.tool.hbm2ddl.DatabaseMetadata@getTableMetadata: table not found: TodoNotification
    INFO  27.08.15 14:45:35.012  org.hibernate.tool.hbm2ddl.DatabaseMetadata@getTableMetadata: table not found: WikiNotification

So I have two tables in my database, WikiNotification and TodoNotification, whereas I only expect one table because of the single table inheritance strategy.

    <hibernate-configuration>
 <session-factory>
        <property name="hibernate.show_sql">false</property>
        <property name="hibernate.format_sql">false</property>
        <property name="hibernate.bytecode.use_reflection_optimizer">false</property>
        <!--  
        <property name="current_session_context_class">thread</property>
        -->
        <property name="hibernate.hbm2ddl.auto">update</property>

       <!-- 
        <property name="hibernate.show_sql">true</property>
        <property name="hibernate.format_sql">true</property>
        <property name="hibernate.use_sql_comments">true</property>
         -->
 </session-factory>
</hibernate-configuration>

DAO configuration file:

<tx:annotation-driven transaction-manager="transactionManager" />

<bean id="transactionManager"
    class="org.springframework.orm.hibernate3.HibernateTransactionManager">
    <property name="sessionFactory">
        <ref local="sessionFactory" />
    </property>
</bean>

<bean id="sessionFactory"
    class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean">
    <property name="hibernateProperties">
        <props>
            <!-- Hibernate dialect can be defined in application context -->
            <prop key="hibernate.dialect">%{smh.hibernate.dialect}</prop>
            <prop key="hibernate.show_sql">false</prop> 
            <prop key="hibernate.hbm2ddl.auto">update</prop> 
            <prop key="hibernate.connection.SetBigStringTryClob">true</prop>
            <prop key="hibernate.jdbc.batch_size">0</prop>
        </props>
    </property>
    <property name="dataSource" ref="dataSource" />
    <property name="packagesToScan">
        <list>
            <value>com.smh.core.domain</value>
            <!--
                <value>com.seti.core.domain.entity.task.Task</value>
            -->
        </list>
    </property>
</bean>
<bean id="multipartResolver"
    class="org.springframework.web.multipart.commons.CommonsMultipartResolver">

    <!-- one of the properties available; the maximum file size in bytes -->
    <property name="maxUploadSize" value="50000000" />
</bean>

<bean id="persistenceExceptionTranslationPostProcessor"  


class="org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor" />

Answer 1

Notification should be abstract . TodoNotification & WikiNotification should have the @Entity annotation.

Answer 2

There are couple of things you need to do:

1. Make sure whatever dialect you are using is correct as per your Oracle Version.
2. You need to add @Entity on all three classes.
3. You need to provide mapping of all classes into your hibermate.cfg file
4. You need to remove "nullable=false" from the sub-classes, because "TODO_ID" will be null when Discriminator.Value= "Wiki" and WikiNotification member values will be Discriminator.Value= "Todo" .
5. As a try, instead of setting hibernate.hbm2ddl.auto to update , try setting it to " create " and then check the result.