Hi Guys,

Any help here would be great.

I have got two classes ChildXMLClassElement and RootElement whic extend XMLClassElement and I decided to use the table per class hierarchy. My mapping file is as such.

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="schemas">
<class name="XMLClassElement" table="XML_CLASS_ELEMENT">
<id name="id" column="XML_CLASS_ELEMENT_ID">
<generator class="increment"/>
</id>
<property name="sourceClassName"/>
<property name="displayOrder"/>
<property name="xmlElementName"/>
<property name="filterConditions"/>
<property name="resultLimit"/>
<property name="sortByProperty"/>
<property name="sortOrder"/>
<property name="sortType"/>
<set name="xmlPropertyElements" inverse="true">
<key column="XML_CLASS_ELEMENT_ID"/>
<one-to-many class="XMLPropertyElement"/>
</set>
<subclass name="ChildXMLClassElement" discriminator-value="CH">
<many-to-one name="parent" column="XML_CLASS_ELEMENT_ID" not-null="true"/>
<many-to-one name="rootElement" column="XML_CLASS_ELEMENT_ID" not-null="true"/>
<set name="childXMLClassElements" inverse="true">
<key column="XML_CLASS_ELEMENT_ID"/>
<one-to-many class="ChildXMLClassElement"/>
</set>
</subclass>
<subclass name="RootElement" discriminator-value="RE">
<many-to-one name="parent" column="SCHEMA_DEFINITION_ID" not-null="true"/>
<set name="childXMLClassElements" inverse="true">
<key column="XML_CLASS_ELEMENT_ID"/>
<one-to-many class="ChildXMLClassElement"/>
</set>
<set name="queries" inverse="true">
<key column="XML_CLASS_ELEMENT_ID"/>
<one-to-many class="Query"/>
</set>
</subclass>
</class>
</hibernate-mapping>

But when I try to run the application I get the following error.

Initial SessionFactory creation failed.org.hibernate.MappingException: No discriminator found for schemas.RootElement. Discriminator is needed when 'single-table-per-hierarchy' is used and a class has subclasses
16:22:40,984 ERROR [EventManagerServlet]:253 - Servlet.service() for servlet EventManagerServlet threw exception
java.lang.ExceptionInInitializerError
at util.HibernateUtil.<clinit>(HibernateUtil.java:18)
at events.EventManagerServlet.doGet(EventManagerServlet.java:29)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:869)
at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:664)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
at java.lang.Thread.run(Unknown Source)
Caused by: org.hibernate.MappingException: No discriminator found for schemas.RootElement. Discriminator is needed when 'single-table-per-hierarchy' is used and a class has subclasses
at org.hibernate.mapping.SingleTableSubclass.validate(SingleTableSubclass.java:41)
at org.hibernate.cfg.Configuration.validate(Configuration.java:1102)
at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1287)
at util.HibernateUtil.<clinit>(HibernateUtil.java:13)
... 17 more

I cannot understand what I am doing wrong here. I have gone through the hibernate documentation but I couldnt find any help there.
Please please please HELP!

Thanks,
pix.

You specified the discriminator value on your subclasses, but forgot to tell the base class what column to use to act as the discriminator. e.g. <discriminator column="xmlElementName" type="string"/> instead of your xmlElementName column definition (assuming xmlElementName is the discriminator, couldn't tell from casual observation).

See http://www.hibernate.org/hib_docs/v3/re ... criminator

I read that in the hibernate tutorial, but i dont understand the concept of what a discriminator should be. I dont know which column i should use and why. Can u please give me a small example.

thanks,
pix.

The discriminator column is the one that determines which subclass is appropriate for the entity. e.g.

The discriminator column is an hibernate internal column.
It tells hibernate what's the class of a row when fetching an object from the database. With this row hibernate will be able to instantiate the right subclass. Don't care for the name of the column just call it discriminator or something like that and everything will be fine.